| 1 |
Multiples of 3 and 5 |
done |
| 2 |
Even Fibonacci numbers |
done |
| 3 |
Largest prime factor |
done |
| 4 |
Largest palindrome product |
done |
| 5 |
Smallest multiple |
done |
| 6 |
Sum square difference |
done |
| 7 |
10001st prime |
done |
| 8 |
Largest product in a series |
done |
| 9 |
Special Pythagorean triplet |
done |
| 10 |
Summation of primes |
done |
| 11 |
Largest product in a grid |
done |
| 12 |
Highly divisible triangular number |
done |
| 13 |
Large sum |
done |
| 14 |
Longest Collatz sequence |
done |
| 15 |
Lattice paths |
done |
| 16 |
Power digit sum |
done |
| 17 |
Number letter counts |
done |
| 18 |
Maximum path sum I |
done |
| 19 |
Counting Sundays |
done |
| 20 |
Factorial digit sum |
done |
| 21 |
Amicable numbers |
done |
| 22 |
Names scores |
done |
| 23 |
Non-abundant sums |
done |
| 24 |
Lexicographic permutations |
done |
| 25 |
1000-digit Fibonacci number |
done |
| 26 |
Reciprocal cycles |
done |
| 27 |
Quadratic primes |
done |
| 28 |
Number spiral diagonals |
done |
| 29 |
Distinct powers |
done |
| 30 |
Digit fifth powers |
done |
| 31 |
Coin sums |
done |
| 32 |
Pandigital products |
done |
| 33 |
Digit cancelling fractions |
done |
| 34 |
Digit factorials |
done |
| 35 |
Circular primes |
done |
| 36 |
Double-base palindromes |
done |
| 37 |
Truncatable primes |
done |
| 38 |
Pandigital multiples |
done |
| 39 |
Integer right triangles |
done |
| 40 |
Champernowne's constant |
done |
| 41 |
Pandigital prime |
done |
| 42 |
Coded triangle numbers |
done |
| 43 |
Sub-string divisibility |
done |
| 44 |
Pentagon numbers |
done |
| 45 |
Triangular, pentagonal, and hexagonal |
done |
| 46 |
Goldbach's other conjecture |
done |
| 47 |
Distinct primes factors |
done |
| 48 |
Self powers |
done |
| 49 |
Prime permutations |
done |
| 50 |
Consecutive prime sum |
done |
| 51 |
Prime digit replacements |
done |
| 52 |
Permuted multiples |
done |
| 53 |
Combinatoric selections |
done |
| 54 |
Poker hands |
done |
| 55 |
Lychrel numbers |
done |
| 56 |
Powerful digit sum |
done |
| 57 |
Square root convergents |
done |
| 58 |
Spiral primes |
done |
| 59 |
XOR decryption |
done |
| 60 |
Prime pair sets |
done |
| 61 |
Cyclical figurate numbers |
done |
| 62 |
Cubic permutations |
done |
| 63 |
Powerful digit counts |
done |
| 64 |
Odd period square roots |
done |
| 65 |
Convergents of e |
done |
| 66 |
Diophantine equation |
done |
| 67 |
Maximum path sum II |
done |
| 68 |
Magic 5-gon ring |
done |
| 69 |
Totient maximum |
done |
| 70 |
Totient permutation |
done |
| 71 |
Ordered fractions |
done |
| 72 |
Counting fractions |
done |
| 73 |
Counting fractions in a range |
needs-optimization |
| 74 |
Digit factorial chains |
needs-optimization |
| 75 |
Singular integer right triangles |
done |
| 76 |
Counting summations |
done |
| 77 |
Prime summations |
done |
| 78 |
Coin partitions |
done |
| 79 |
Passcode derivation |
done |
| 80 |
Square root digital expansion |
done |
| 81 |
Path sum: two ways |
done |
| 82 |
Path sum: three ways |
done |
| 83 |
Path sum: four ways |
in-progress |
| 84 |
Monopoly odds |
not-attempted |
| 85 |
Counting rectangles |
done |
| 86 |
Cuboid route |
not-attempted |
| 87 |
Prime power triples |
not-attempted |
| 88 |
Product-sum numbers |
not-attempted |
| 89 |
Roman numerals |
not-attempted |
| 90 |
Cube digit pairs |
not-attempted |
| 91 |
Right triangles with integer coordinates |
not-attempted |
| 92 |
Square digit chains |
done |
| 93 |
Arithmetic expressions |
not-attempted |
| 94 |
Almost equilateral triangles |
not-attempted |
| 95 |
Amicable chains |
not-attempted |
| 96 |
Su Doku |
not-attempted |
| 97 |
Large non-Mersenne prime |
done |
| 98 |
Anagramic squares |
not-attempted |
| 99 |
Largest exponential |
not-attempted |
| 100 |
Arranged probability |
not-attempted |
| 101 |
Optimum polynomial |
not-attempted |
| 102 |
Triangle containment |
not-attempted |
| 103 |
Special subset sums: optimum |
not-attempted |
| 104 |
Pandigital Fibonacci ends |
not-attempted |
| 105 |
Special subset sums: testing |
not-attempted |
| 106 |
Special subset sums: meta-testing |
not-attempted |
| 107 |
Minimal network |
not-attempted |
| 108 |
Diophantine reciprocals I |
done |
| 109 |
Darts |
not-attempted |
| 110 |
Diophantine reciprocals II |
done |
| 111 |
Primes with runs |
not-attempted |
| 112 |
Bouncy numbers |
not-attempted |
| 113 |
Non-bouncy numbers |
not-attempted |
| 114 |
Counting block combinations I |
not-attempted |
| 115 |
Counting block combinations II |
not-attempted |
| 116 |
Red, green or blue tiles |
not-attempted |
| 117 |
Red, green, and blue tiles |
not-attempted |
| 118 |
Pandigital prime sets |
not-attempted |
| 119 |
Digit power sum |
not-attempted |
| 120 |
Square remainders |
not-attempted |
| 121 |
Disc game prize fund |
not-attempted |
| 122 |
Efficient exponentiation |
not-attempted |
| 123 |
Prime square remainders |
not-attempted |
| 124 |
Ordered radicals |
not-attempted |
| 125 |
Palindromic sums |
not-attempted |
| 126 |
Cuboid layers |
not-attempted |
| 127 |
abc-hits |
not-attempted |
| 128 |
Hexagonal tile differences |
not-attempted |
| 129 |
Repunit divisibility |
not-attempted |
| 130 |
Composites with prime repunit property |
not-attempted |
| 131 |
Prime cube partnership |
not-attempted |
| 132 |
Large repunit factors |
not-attempted |
| 133 |
Repunit nonfactors |
not-attempted |
| 134 |
Prime pair connection |
not-attempted |
| 135 |
Same differences |
not-attempted |
| 136 |
Singleton difference |
not-attempted |
| 137 |
Fibonacci golden nuggets |
not-attempted |
| 138 |
Special isosceles triangles |
not-attempted |
| 139 |
Pythagorean tiles |
not-attempted |
| 140 |
Modified Fibonacci golden nuggets |
not-attempted |
| 141 |
Investigating progressive numbers, n, which are also square |
not-attempted |
| 142 |
Perfect Square Collection |
not-attempted |
| 143 |
Investigating the Torricelli point of a triangle |
not-attempted |
| 144 |
Investigating multiple reflections of a laser beam |
not-attempted |
| 145 |
How many reversible numbers are there below one-billion? |
not-attempted |
| 146 |
Investigating a Prime Pattern |
not-attempted |
| 147 |
Rectangles in cross-hatched grids |
not-attempted |
| 148 |
Exploring Pascal's triangle |
not-attempted |
| 149 |
Searching for a maximum-sum subsequence |
not-attempted |
| 150 |
Searching a triangular array for a sub-triangle having minimum-sum |
not-attempted |
| 151 |
Paper sheets of standard sizes: an expected-value problem |
not-attempted |
| 152 |
Writing 1/2 as a sum of inverse squares |
not-attempted |
| 153 |
Investigating Gaussian Integers |
not-attempted |
| 154 |
Exploring Pascal's pyramid |
not-attempted |
| 155 |
Counting Capacitor Circuits |
not-attempted |
| 156 |
Counting Digits |
not-attempted |
| 157 |
Solving the diophantine equation 1/a+1/b= p/10n |
not-attempted |
| 158 |
Exploring strings for which only one character comes lexicographically after its neighbour to the left |
not-attempted |
| 159 |
Digital root sums of factorisations |
not-attempted |
| 160 |
Factorial trailing digits |
not-attempted |
| 161 |
Triominoes |
not-attempted |
| 162 |
Hexadecimal numbers |
not-attempted |
| 163 |
Cross-hatched triangles |
not-attempted |
| 164 |
Numbers for which no three consecutive digits have a sum greater than a given value |
not-attempted |
| 165 |
Intersections |
not-attempted |
| 166 |
Criss Cross |
not-attempted |
| 167 |
Investigating Ulam sequences |
not-attempted |
| 168 |
Number Rotations |
not-attempted |
| 169 |
Exploring the number of different ways a number can be expressed as a sum of powers of 2 |
not-attempted |
| 170 |
Find the largest 0 to 9 pandigital that can be formed by concatenating products |
not-attempted |
| 171 |
Finding numbers for which the sum of the squares of the digits is a square |
not-attempted |
| 172 |
Investigating numbers with few repeated digits |
not-attempted |
| 173 |
Using up to one million tiles how many different "hollow" square laminae can be formed? |
not-attempted |
| 174 |
Counting the number of "hollow" square laminae that can form one, two, three, ... distinct arrangements |
not-attempted |
| 175 |
Fractions involving the number of different ways a number can be expressed as a sum of powers of 2 |
not-attempted |
| 176 |
Right-angled triangles that share a cathetus |
not-attempted |
| 177 |
Integer angled Quadrilaterals |
not-attempted |
| 178 |
Step Numbers |
not-attempted |
| 179 |
Consecutive positive divisors |
not-attempted |
| 180 |
Rational zeros of a function of three variables |
not-attempted |
| 181 |
Investigating in how many ways objects of two different colours can be grouped |
not-attempted |
| 182 |
RSA encryption |
not-attempted |
| 183 |
Maximum product of parts |
not-attempted |
| 184 |
Triangles containing the origin |
not-attempted |
| 185 |
Number Mind |
not-attempted |
| 186 |
Connectedness of a network |
not-attempted |
| 187 |
Semiprimes |
not-attempted |
| 188 |
The hyperexponentiation of a number |
not-attempted |
| 189 |
Tri-colouring a triangular grid |
not-attempted |
| 190 |
Maximising a weighted product |
not-attempted |
| 191 |
Prize Strings |
not-attempted |
| 192 |
Best Approximations |
not-attempted |
| 193 |
Squarefree Numbers |
not-attempted |
| 194 |
Coloured Configurations |
not-attempted |
| 195 |
Inscribed circles of triangles with one angle of 60 degrees |
not-attempted |
| 196 |
Prime triplets |
not-attempted |
| 197 |
Investigating the behaviour of a recursively defined sequence |
not-attempted |
| 198 |
Ambiguous Numbers |
not-attempted |
| 199 |
Iterative Circle Packing |
not-attempted |
| 200 |
Find the 200th prime-proof sqube containing the contiguous sub-string "200" |
not-attempted |
| 201 |
Subsets with a unique sum |
not-attempted |
| 202 |
Laserbeam |
not-attempted |
| 203 |
Squarefree Binomial Coefficients |
not-attempted |
| 204 |
Generalised Hamming Numbers |
not-attempted |
| 205 |
Dice Game |
not-attempted |
| 206 |
Concealed Square |
not-attempted |
| 207 |
Integer partition equations |
not-attempted |
| 208 |
Robot Walks |
not-attempted |
| 209 |
Circular Logic |
not-attempted |
| 210 |
Obtuse Angled Triangles |
not-attempted |
| 211 |
Divisor Square Sum |
not-attempted |
| 212 |
Combined Volume of Cuboids |
not-attempted |
| 213 |
Flea Circus |
not-attempted |
| 214 |
Totient Chains |
not-attempted |
| 215 |
Crack-free Walls |
not-attempted |
| 216 |
Investigating the primality of numbers of the form 2n2-1 |
not-attempted |
| 217 |
Balanced Numbers |
not-attempted |
| 218 |
Perfect right-angled triangles |
not-attempted |
| 219 |
Skew-cost coding |
not-attempted |
| 220 |
Heighway Dragon |
not-attempted |
| 221 |
Alexandrian Integers |
not-attempted |
| 222 |
Sphere Packing |
not-attempted |
| 223 |
Almost right-angled triangles I |
not-attempted |
| 224 |
Almost right-angled triangles II |
not-attempted |
| 225 |
Tribonacci non-divisors |
not-attempted |
| 226 |
A Scoop of Blancmange |
not-attempted |
| 227 |
The Chase |
not-attempted |
| 228 |
Minkowski Sums |
not-attempted |
| 229 |
Four Representations using Squares |
not-attempted |
| 230 |
Fibonacci Words |
not-attempted |
| 231 |
The prime factorisation of binomial coefficients |
not-attempted |
| 232 |
The Race |
not-attempted |
| 233 |
Lattice points on a circle |
not-attempted |
| 234 |
Semidivisible numbers |
not-attempted |
| 235 |
An Arithmetic Geometric sequence |
not-attempted |
| 236 |
Luxury Hampers |
not-attempted |
| 237 |
Tours on a 4 x n playing board |
not-attempted |
| 238 |
Infinite string tour |
not-attempted |
| 239 |
Twenty-two Foolish Primes |
not-attempted |
| 240 |
Top Dice |
not-attempted |
| 241 |
Perfection Quotients |
not-attempted |
| 242 |
Odd Triplets |
not-attempted |
| 243 |
Resilience |
not-attempted |
| 244 |
Sliders |
not-attempted |
| 245 |
Coresilience |
not-attempted |
| 246 |
Tangents to an ellipse |
not-attempted |
| 247 |
Squares under a hyperbola |
not-attempted |
| 248 |
Numbers for which Euler’s totient function equals 13! |
not-attempted |
| 249 |
Prime Subset Sums |
not-attempted |
| 250 |
250250 |
not-attempted |
| 251 |
Cardano Triplets |
not-attempted |
| 252 |
Convex Holes |
not-attempted |
| 253 |
Tidying up |
not-attempted |
| 254 |
Sums of Digit Factorials |
not-attempted |
| 255 |
Rounded Square Roots |
not-attempted |
| 256 |
Tatami-Free Rooms |
not-attempted |
| 257 |
Angular Bisectors |
not-attempted |
| 258 |
A lagged Fibonacci sequence |
not-attempted |
| 259 |
Reachable Numbers |
not-attempted |
| 260 |
Stone Game |
not-attempted |
| 261 |
Pivotal Square Sums |
not-attempted |
| 262 |
Mountain Range |
not-attempted |
| 263 |
An engineers' dream come true |
not-attempted |
| 264 |
Triangle Centres |
not-attempted |
| 265 |
Binary Circles |
not-attempted |
| 266 |
Pseudo Square Root |
not-attempted |
| 267 |
Billionaire |
not-attempted |
| 268 |
Counting numbers with at least four distinct prime factors less than 100 |
not-attempted |
| 269 |
Polynomials with at least one integer root |
not-attempted |
| 270 |
Cutting Squares |
not-attempted |
| 271 |
Modular Cubes, part 1 |
not-attempted |
| 272 |
Modular Cubes, part 2 |
not-attempted |
| 273 |
Sum of Squares |
not-attempted |
| 274 |
Divisibility Multipliers |
not-attempted |
| 275 |
Balanced Sculptures |
not-attempted |
| 276 |
Primitive Triangles |
not-attempted |
| 277 |
A Modified Collatz sequence |
not-attempted |
| 278 |
Linear Combinations of Semiprimes |
not-attempted |
| 279 |
Triangles with integral sides and an integral angle |
not-attempted |
| 280 |
Ant and seeds |
not-attempted |
| 281 |
Pizza Toppings |
not-attempted |
| 282 |
The Ackermann function |
not-attempted |
| 283 |
Integer sided triangles for which the area/perimeter ratio is integral |
not-attempted |
| 284 |
Steady Squares |
not-attempted |
| 285 |
Pythagorean odds |
not-attempted |
| 286 |
Scoring probabilities |
not-attempted |
| 287 |
Quadtree encoding (a simple compression algorithm) |
not-attempted |
| 288 |
An enormous factorial |
not-attempted |
| 289 |
Eulerian Cycles |
not-attempted |
| 290 |
Digital Signature |
not-attempted |
| 291 |
Panaitopol Primes |
not-attempted |
| 292 |
Pythagorean Polygons |
not-attempted |
| 293 |
Pseudo-Fortunate Numbers |
not-attempted |
| 294 |
Sum of digits - experience #23 |
not-attempted |
| 295 |
Lenticular holes |
not-attempted |
| 296 |
Angular Bisector and Tangent |
not-attempted |
| 297 |
Zeckendorf Representation |
not-attempted |
| 298 |
Selective Amnesia |
not-attempted |
| 299 |
Three similar triangles |
not-attempted |
| 300 |
Protein folding |
not-attempted |
| 301 |
Nim |
not-attempted |
| 302 |
Strong Achilles Numbers |
not-attempted |
| 303 |
Multiples with small digits |
not-attempted |
| 304 |
Primonacci |
not-attempted |
| 305 |
Reflexive Position |
not-attempted |
| 306 |
Paper-strip Game |
not-attempted |
| 307 |
Chip Defects |
not-attempted |
| 308 |
An amazing Prime-generating Automaton |
not-attempted |
| 309 |
Integer Ladders |
not-attempted |
| 310 |
Nim Square |
not-attempted |
| 311 |
Biclinic Integral Quadrilaterals |
not-attempted |
| 312 |
Cyclic paths on Sierpiński graphs |
not-attempted |
| 313 |
Sliding game |
not-attempted |
| 314 |
The Mouse on the Moon |
not-attempted |
| 315 |
Digital root clocks |
not-attempted |
| 316 |
Numbers in decimal expansions |
not-attempted |
| 317 |
Firecracker |
not-attempted |
| 318 |
2011 nines |
not-attempted |
| 319 |
Bounded Sequences |
not-attempted |
| 320 |
Factorials divisible by a huge integer |
not-attempted |
| 321 |
Swapping Counters |
not-attempted |
| 322 |
Binomial coefficients divisible by 10 |
not-attempted |
| 323 |
Bitwise-OR operations on random integers |
not-attempted |
| 324 |
Building a tower |
not-attempted |
| 325 |
Stone Game II |
not-attempted |
| 326 |
Modulo Summations |
not-attempted |
| 327 |
Rooms of Doom |
not-attempted |
| 328 |
Lowest-cost Search |
not-attempted |
| 329 |
Prime Frog |
not-attempted |
| 330 |
Euler's Number |
not-attempted |
| 331 |
Cross flips |
not-attempted |
| 332 |
Spherical triangles |
not-attempted |
| 333 |
Special partitions |
not-attempted |
| 334 |
Spilling the beans |
not-attempted |
| 335 |
Gathering the beans |
not-attempted |
| 336 |
Maximix Arrangements |
not-attempted |
| 337 |
Totient Stairstep Sequences |
not-attempted |
| 338 |
Cutting Rectangular Grid Paper |
not-attempted |
| 339 |
Peredur fab Efrawg |
not-attempted |
| 340 |
Crazy Function |
not-attempted |
| 341 |
Golomb's self-describing sequence |
not-attempted |
| 342 |
The totient of a square is a cube |
not-attempted |
| 343 |
Fractional Sequences |
not-attempted |
| 344 |
Silver dollar game |
not-attempted |
| 345 |
Matrix Sum |
not-attempted |
| 346 |
Strong Repunits |
not-attempted |
| 347 |
Largest integer divisible by two primes |
not-attempted |
| 348 |
Sum of a square and a cube |
not-attempted |
| 349 |
Langton's ant |
not-attempted |
| 350 |
Constraining the least greatest and the greatest least |
not-attempted |
| 351 |
Hexagonal orchards |
not-attempted |
| 352 |
Blood tests |
not-attempted |
| 353 |
Risky moon |
not-attempted |
| 354 |
Distances in a bee's honeycomb |
not-attempted |
| 355 |
Maximal coprime subset |
not-attempted |
| 356 |
Largest roots of cubic polynomials |
not-attempted |
| 357 |
Prime generating integers |
done |
| 358 |
Cyclic numbers |
not-attempted |
| 359 |
Hilbert's New Hotel |
not-attempted |
| 360 |
Scary Sphere |
not-attempted |
| 361 |
Subsequence of Thue-Morse sequence |
not-attempted |
| 362 |
Squarefree factors |
not-attempted |
| 363 |
Bézier Curves |
not-attempted |
| 364 |
Comfortable distance |
not-attempted |
| 365 |
A huge binomial coefficient |
not-attempted |
| 366 |
Stone Game III |
not-attempted |
| 367 |
Bozo sort |
not-attempted |
| 368 |
A Kempner-like series |
not-attempted |
| 369 |
Badugi |
not-attempted |
| 370 |
Geometric triangles |
not-attempted |
| 371 |
Licence plates |
not-attempted |
| 372 |
Pencils of rays |
not-attempted |
| 373 |
Circumscribed Circles |
not-attempted |
| 374 |
Maximum Integer Partition Product |
not-attempted |
| 375 |
Minimum of subsequences |
not-attempted |
| 376 |
Nontransitive sets of dice |
not-attempted |
| 377 |
Sum of digits, experience 13 |
not-attempted |
| 378 |
Triangle Triples |
not-attempted |
| 379 |
Least common multiple count |
not-attempted |
| 380 |
Amazing Mazes! |
not-attempted |
| 381 |
(prime-k) factorial |
not-attempted |
| 382 |
Generating polygons |
not-attempted |
| 383 |
Divisibility comparison between factorials |
not-attempted |
| 384 |
Rudin-Shapiro sequence |
not-attempted |
| 385 |
Ellipses inside triangles |
not-attempted |
| 386 |
Maximum length of an antichain |
not-attempted |
| 387 |
Harshad Numbers |
not-attempted |
| 388 |
Distinct Lines |
not-attempted |
| 389 |
Platonic Dice |
not-attempted |
| 390 |
Triangles with non rational sides and integral area |
not-attempted |
| 391 |
Hopping Game |
not-attempted |
| 392 |
Enmeshed unit circle |
not-attempted |
| 393 |
Migrating ants |
not-attempted |
| 394 |
Eating pie |
not-attempted |
| 395 |
Pythagorean tree |
not-attempted |
| 396 |
Weak Goodstein sequence |
not-attempted |
| 397 |
Triangle on parabola |
not-attempted |
| 398 |
Cutting rope |
not-attempted |
| 399 |
Squarefree Fibonacci Numbers |
not-attempted |
| 400 |
Fibonacci tree game |
not-attempted |
| 401 |
Sum of squares of divisors |
not-attempted |
| 402 |
Integer-valued polynomials |
not-attempted |
| 403 |
Lattice points enclosed by parabola and line |
not-attempted |
| 404 |
Crisscross Ellipses |
not-attempted |
| 405 |
A rectangular tiling |
not-attempted |
| 406 |
Guessing Game |
not-attempted |
| 407 |
Idempotents |
not-attempted |
| 408 |
Admissible paths through a grid |
not-attempted |
| 409 |
Nim Extreme |
not-attempted |
| 410 |
Circle and tangent line |
not-attempted |
| 411 |
Uphill paths |
not-attempted |
| 412 |
Gnomon numbering |
not-attempted |
| 413 |
One-child Numbers |
not-attempted |
| 414 |
Kaprekar constant |
not-attempted |
| 415 |
Titanic sets |
not-attempted |
| 416 |
A frog's trip |
not-attempted |
| 417 |
Reciprocal cycles II |
not-attempted |
| 418 |
Factorisation triples |
not-attempted |
| 419 |
Look and say sequence |
not-attempted |
| 420 |
2x2 positive integer matrix |
not-attempted |
| 421 |
Prime factors of n15+1 |
not-attempted |
| 422 |
Sequence of points on a hyperbola |
not-attempted |
| 423 |
Consecutive die throws |
not-attempted |
| 424 |
Kakuro |
not-attempted |
| 425 |
Prime connection |
not-attempted |
| 426 |
Box-ball system |
not-attempted |
| 427 |
n-sequences |
not-attempted |
| 428 |
Necklace of circles |
not-attempted |
| 429 |
Sum of squares of unitary divisors |
not-attempted |
| 430 |
Range flips |
not-attempted |
| 431 |
Square Space Silo |
not-attempted |
| 432 |
Totient sum |
not-attempted |
| 433 |
Steps in Euclid's algorithm |
not-attempted |
| 434 |
Rigid graphs |
not-attempted |
| 435 |
Polynomials of Fibonacci numbers |
not-attempted |
| 436 |
Unfair wager |
not-attempted |
| 437 |
Fibonacci primitive roots |
not-attempted |
| 438 |
Integer part of polynomial equation's solutions |
not-attempted |
| 439 |
Sum of sum of divisors |
not-attempted |
| 440 |
GCD and Tiling |
not-attempted |
| 441 |
The inverse summation of coprime couples |
not-attempted |
| 442 |
Eleven-free integers |
not-attempted |
| 443 |
GCD sequence |
not-attempted |
| 444 |
The Roundtable Lottery |
not-attempted |
| 445 |
Retractions A |
not-attempted |
| 446 |
Retractions B |
not-attempted |
| 447 |
Retractions C |
not-attempted |
| 448 |
Average least common multiple |
not-attempted |
| 449 |
Chocolate covered candy |
not-attempted |
| 450 |
Hypocycloid and Lattice points |
not-attempted |
| 451 |
Modular inverses |
not-attempted |
| 452 |
Long Products |
not-attempted |
| 453 |
Lattice Quadrilaterals |
not-attempted |
| 454 |
Diophantine reciprocals III |
not-attempted |
| 455 |
Powers With Trailing Digits |
not-attempted |
| 456 |
Triangles containing the origin II |
not-attempted |
| 457 |
A polynomial modulo the square of a prime |
not-attempted |
| 458 |
Permutations of Project |
not-attempted |
| 459 |
Flipping game |
not-attempted |
| 460 |
An ant on the move |
not-attempted |
| 461 |
Almost Pi |
not-attempted |
| 462 |
Permutation of 3-smooth numbers |
not-attempted |
| 463 |
A weird recurrence relation |
not-attempted |
| 464 |
Möbius function and intervals |
not-attempted |
| 465 |
Polar polygons |
not-attempted |
| 466 |
Distinct terms in a multiplication table |
not-attempted |
| 467 |
Superinteger |
not-attempted |
| 468 |
Smooth divisors of binomial coefficients |
not-attempted |
| 469 |
Empty chairs |
not-attempted |
| 470 |
Super Ramvok |
not-attempted |
| 471 |
Triangle inscribed in ellipse |
not-attempted |
| 472 |
Comfortable Distance II |
not-attempted |
| 473 |
Phigital number base |
not-attempted |
| 474 |
Last digits of divisors |
not-attempted |
| 475 |
Music festival |
not-attempted |
| 476 |
Circle Packing II |
not-attempted |
| 477 |
Number Sequence Game |
not-attempted |
| 478 |
Mixtures |
not-attempted |
| 479 |
Roots on the Rise |
not-attempted |
| 480 |
The Last Question |
not-attempted |
| 481 |
Chef Showdown |
not-attempted |
| 482 |
The incenter of a triangle |
not-attempted |
| 483 |
Repeated permutation |
not-attempted |
| 484 |
Arithmetic Derivative |
not-attempted |
| 485 |
Maximum number of divisors |
not-attempted |
| 486 |
Palindrome-containing strings |
not-attempted |
| 487 |
Sums of power sums |
not-attempted |
| 488 |
Unbalanced Nim |
not-attempted |
| 489 |
Common factors between two sequences |
not-attempted |
| 490 |
Jumping frog |
not-attempted |
| 491 |
Double pandigital number divisible by 11 |
not-attempted |
| 492 |
Exploding sequence |
not-attempted |
| 493 |
Under The Rainbow |
not-attempted |
| 494 |
Collatz prefix families |
not-attempted |
| 495 |
Writing n as the product of k distinct positive integers |
not-attempted |
| 496 |
Incenter and circumcenter of triangle |
not-attempted |
| 497 |
Drunken Tower of Hanoi |
not-attempted |
| 498 |
Remainder of polynomial division |
not-attempted |
| 499 |
St. Petersburg Lottery |
not-attempted |
| 500 |
Problem 500!!! |
not-attempted |
| 501 |
Eight Divisors |
not-attempted |
| 502 |
Counting Castles |
not-attempted |
| 503 |
Compromise or persist |
not-attempted |
| 504 |
Square on the Inside |
not-attempted |
| 505 |
Bidirectional Recurrence |
not-attempted |
| 506 |
Clock sequence |
not-attempted |
| 507 |
Shortest Lattice Vector |
not-attempted |
| 508 |
Integers in base i-1 |
not-attempted |
| 509 |
Divisor Nim |
not-attempted |
| 510 |
Tangent Circles |
not-attempted |
| 511 |
Sequences with nice divisibility properties |
not-attempted |
| 512 |
Sums of totients of powers |
not-attempted |
| 513 |
Integral median |
not-attempted |
| 514 |
Geoboard Shapes |
not-attempted |
| 515 |
Dissonant Numbers |
not-attempted |
| 516 |
5-smooth totients |
not-attempted |
| 517 |
A real recursion |
not-attempted |
| 518 |
Prime triples and geometric sequences |
not-attempted |
| 519 |
Tricoloured Coin Fountains |
not-attempted |
| 520 |
Simbers |
not-attempted |
| 521 |
Smallest prime factor |
not-attempted |
| 522 |
Hilbert's Blackout |
not-attempted |
| 523 |
First Sort I |
not-attempted |
| 524 |
First Sort II |
not-attempted |
| 525 |
Rolling Ellipse |
not-attempted |
| 526 |
Largest prime factors of consecutive numbers |
not-attempted |
| 527 |
Randomized Binary Search |
not-attempted |
| 528 |
Constrained Sums |
not-attempted |
| 529 |
10-substrings |
not-attempted |
| 530 |
GCD of Divisors |
not-attempted |
| 531 |
Chinese leftovers |
not-attempted |
| 532 |
Nanobots on Geodesics |
not-attempted |
| 533 |
Minimum values of the Carmichael function |
not-attempted |
| 534 |
Weak Queens |
not-attempted |
| 535 |
Fractal Sequence |
not-attempted |
| 536 |
Modulo power identity |
not-attempted |
| 537 |
Counting tuples |
not-attempted |
| 538 |
Maximum quadrilaterals |
not-attempted |
| 539 |
Odd elimination |
not-attempted |
| 540 |
Counting primitive Pythagorean triples |
not-attempted |
| 541 |
Divisibility of Harmonic Number Denominators |
not-attempted |
| 542 |
Geometric Progression with Maximum Sum |
not-attempted |
| 543 |
Prime-Sum Numbers |
not-attempted |
| 544 |
Chromatic Conundrum |
not-attempted |
| 545 |
Faulhaber's Formulas |
not-attempted |
| 546 |
The Floor's Revenge |
not-attempted |
| 547 |
Distance of random points within hollow square laminae |
not-attempted |
| 548 |
Gozinta Chains |
not-attempted |
| 549 |
Divisibility of factorials |
not-attempted |
| 550 |
Divisor game |
not-attempted |
| 551 |
Sum of digits sequence |
not-attempted |
| 552 |
Chinese leftovers II |
not-attempted |
| 553 |
Power sets of power sets |
not-attempted |
| 554 |
Centaurs on a chess board |
not-attempted |
| 555 |
McCarthy 91 function |
not-attempted |
| 556 |
Squarefree Gaussian Integers |
not-attempted |
| 557 |
Cutting triangles |
not-attempted |
| 558 |
Irrational base |
not-attempted |
| 559 |
Permuted Matrices |
not-attempted |
| 560 |
Coprime Nim |
not-attempted |
| 561 |
Divisor Pairs |
not-attempted |
| 562 |
Maximal perimeter |
not-attempted |
| 563 |
Robot Welders |
not-attempted |
| 564 |
Maximal polygons |
not-attempted |
| 565 |
Divisibility of sum of divisors |
not-attempted |
| 566 |
Cake Icing Puzzle |
not-attempted |
| 567 |
Reciprocal games I |
not-attempted |
| 568 |
Reciprocal games II |
not-attempted |
| 569 |
Prime Mountain Range |
not-attempted |
| 570 |
Snowflakes |
not-attempted |
| 571 |
Super Pandigital Numbers |
not-attempted |
| 572 |
Idempotent matrices |
not-attempted |
| 573 |
Unfair race |
not-attempted |
| 574 |
Verifying Primes |
not-attempted |
| 575 |
Wandering Robots |
not-attempted |
| 576 |
Irrational jumps |
not-attempted |
| 577 |
Counting hexagons |
not-attempted |
| 578 |
Integers with decreasing prime powers |
not-attempted |
| 579 |
Lattice points in lattice cubes |
not-attempted |
| 580 |
Squarefree Hilbert numbers |
not-attempted |
| 581 |
47-smooth triangular numbers |
not-attempted |
| 582 |
Nearly isosceles 120 degree triangles |
not-attempted |
| 583 |
Heron Envelopes |
not-attempted |
| 584 |
Birthday Problem Revisited |
not-attempted |
| 585 |
Nested square roots |
not-attempted |
| 586 |
Binary Quadratic Form |
not-attempted |
| 587 |
Concave triangle |
not-attempted |
| 588 |
Quintinomial coefficients |
not-attempted |
| 589 |
Poohsticks Marathon |
not-attempted |
| 590 |
Sets with a given Least Common Multiple |
not-attempted |
| 591 |
Best Approximations by Quadratic Integers |
not-attempted |
| 592 |
Factorial trailing digits 2 |
not-attempted |
| 593 |
Fleeting Medians |
not-attempted |
| 594 |
Rhombus Tilings |
not-attempted |
| 595 |
Incremental Random Sort |
not-attempted |
| 596 |
Number of lattice points in a hyperball |
not-attempted |
| 597 |
Torpids |
not-attempted |
| 598 |
Split Divisibilities |
not-attempted |
| 599 |
Distinct Colourings of a Rubik's Cube |
not-attempted |
| 600 |
Integer sided equiangular hexagons |
not-attempted |
| 601 |
Divisibility streaks |
not-attempted |
| 602 |
Product of Head Counts |
not-attempted |
| 603 |
Substring sums of prime concatenations |
not-attempted |
| 604 |
Convex path in square |
not-attempted |
| 605 |
Pairwise Coin-Tossing Game |
not-attempted |
| 606 |
Gozinta Chains II |
not-attempted |
| 607 |
Marsh Crossing |
not-attempted |
| 608 |
Divisor Sums |
not-attempted |
| 609 |
π sequences |
not-attempted |
| 610 |
Roman Numerals II |
not-attempted |
| 611 |
Hallway of square steps |
not-attempted |
| 612 |
Friend numbers |
not-attempted |
| 613 |
Pythagorean Ant |
not-attempted |
| 614 |
Special partitions 2 |
not-attempted |
| 615 |
The millionth number with at least one million prime factors |
not-attempted |
| 616 |
Creative numbers |
not-attempted |
| 617 |
Mirror Power Sequence |
not-attempted |
| 618 |
Numbers with a given prime factor sum |
not-attempted |
| 619 |
Square subsets |
not-attempted |
| 620 |
Planetary Gears |
not-attempted |
| 621 |
Expressing an integer as the sum of triangular numbers |
not-attempted |
| 622 |
Riffle Shuffles |
not-attempted |
| 623 |
Lambda Count |
not-attempted |
| 624 |
Two heads are better than one |
not-attempted |
| 625 |
Gcd sum |
not-attempted |
| 626 |
Counting Binary Matrices |
not-attempted |
| 627 |
Counting products |
not-attempted |
| 628 |
Open chess positions |
not-attempted |
| 629 |
Scatterstone Nim |
not-attempted |
| 630 |
Crossed lines |
not-attempted |
| 631 |
Constrained Permutations |
not-attempted |
| 632 |
Square prime factors |
not-attempted |
| 633 |
Square prime factors II |
not-attempted |
| 634 |
Numbers of the form $a^2b^3$ |
not-attempted |
| 635 |
Subset sums |
not-attempted |
| 636 |
Restricted Factorisations |
not-attempted |
| 637 |
Flexible digit sum |
not-attempted |
| 638 |
Weighted lattice paths |
not-attempted |
| 639 |
Summing a multiplicative function |
not-attempted |
| 640 |
Shut the Box |
not-attempted |
| 641 |
A Long Row of Dice |
not-attempted |
| 642 |
Sum of largest prime factors |
not-attempted |
| 643 |
2-Friendly |
not-attempted |
| 644 |
Squares on the line |
not-attempted |
| 645 |
Every Day is a Holiday |
not-attempted |
| 646 |
Bounded Divisors |
not-attempted |
| 647 |
Linear Transformations of Polygonal Numbers |
not-attempted |
| 648 |
Skipping Squares |
not-attempted |
| 649 |
Low-Prime Chessboard Nim |
not-attempted |
| 650 |
Divisors of Binomial Product |
not-attempted |
| 651 |
Patterned Cylinders |
not-attempted |
| 652 |
Distinct values of a proto-logarithmic function |
not-attempted |
| 653 |
Frictionless Tube |
not-attempted |
| 654 |
Neighbourly Constraints |
not-attempted |
| 655 |
Divisible Palindromes |
not-attempted |
| 656 |
Palindromic sequences |
not-attempted |
| 657 |
Incomplete words |
not-attempted |
| 658 |
Incomplete words II |
not-attempted |
| 659 |
Largest prime |
not-attempted |
| 660 |
Pandigital Triangles |
not-attempted |
| 661 |
A Long Chess Match |
not-attempted |
| 662 |
Fibonacci paths |
not-attempted |
| 663 |
Sums of subarrays |
not-attempted |
| 664 |
An infinite game |
not-attempted |
| 665 |
Proportionate Nim |
not-attempted |
| 666 |
Polymorphic Bacteria |
not-attempted |
| 667 |
Moving Pentagon |
experimentation |
| 668 |
Square root smooth Numbers |
experimentation |
| 669 |
The King's Banquet |
not-attempted |
| 670 |
Colouring a Strip |
not-attempted |
| 671 |
Colouring a Loop |
not-attempted |
| 672 |
One more one |
not-attempted |
| 673 |
Beds and Desks |
not-attempted |
| 674 |
Solving $\mathcal{I}$-equations |
not-attempted |
| 675 |
$2^{\omega(n)}$ |
not-attempted |
