Problems

These problems are part of Project Euler and are licensed under CC BY-NC-SA 2.0 UK

1. Multiples of 3 and 5 Clojurians @ Thu, 27 Aug 2015, NASA @ Thu, 02 Apr 2015, 99 Problems @ Mon, 29 Apr 2013, I got %d problems but a %s ain't one @ Thu, 01 May 2014, Python @ Fri, 26 Feb 2016, PDV @ Fri, 26 Feb 2016, Team SNAP! @ Thu, 31 Mar 2016, Team🍕 @ Wed, 28 Sep 2016, Prime Triplets @ Thu, 11 May 2017, Angry Armadillos @ Fri, 30 Jan 2015, We'll Tell You A Name Later @ Thu, 30 Jan 2014, Sandstorm @ Thu, 30 Jan 2014, Candy Cane @ Thu, 12 Dec 2013, 1 @ Thu, 27 Mar 2014, Project Humbug @ Thu, 12 Dec 2013, Hung Like David Foster Wallace @ Thu, 12 Dec 2013, Uno Punto @ Thu, 29 Aug 2013, One Point @ Thu, 29 Aug 2013, C# @ Thu, 29 Aug 2013, Team this.Table @ Thu, 25 Jun 2015, Team Beer @ Thu, 28 Aug 2014, C++ @ Thu, 29 Aug 2013, C @ Thu, 29 Aug 2013, Not As Good As Clojure @ Thu, 29 Oct 2015, The 26ers @ Thu, 28 Jul 2016, Mighty Morphin' Power Angers @ Fri, 30 Jan 2015, Cauliflower @ Thu, 28 Jul 2016, Tits McGee @ Thu, 12 Dec 2013, ShanMan @ Thu, 30 May 2013, Precise Pangolin @ Thu, 29 May 2014, Fünke @ Thu, 30 May 2013, Rock Solid @ Thu, 02 Apr 2015, Jesscici @ Fri, 26 Feb 2016, Clojing Time @ Thu, 27 Feb 2014, Kepler @ Thu, 30 May 2013, Brian @ Thu, 30 May 2013, Higi @ Mon, 29 Apr 2013, Geminy Cricket @ Thu, 28 May 2015, PotionMasters @ Thu, 25 Sep 2014, Dragon Fruit @ Mon, 29 Apr 2013, Four Balls @ Thu, 28 May 2015, Persona 4 @ Thu, 30 Oct 2014
2. Even Fibonacci numbers Team🍕 @ Wed, 28 Sep 2016, Geminy Cricket @ Thu, 28 May 2015, Persona 4 @ Thu, 30 Oct 2014, max(pow(e,r)) @ Thu, 28 Aug 2014, 99 Problems @ Mon, 29 Apr 2013, Rock Solid @ Thu, 02 Apr 2015, NASA @ Thu, 02 Apr 2015, Dragon Fruit @ Mon, 29 Apr 2013, Higi @ Mon, 29 Apr 2013, Precise Pangolin @ Thu, 29 May 2014, Brian @ Thu, 30 May 2013, Kepler @ Thu, 30 May 2013, Clojing Time @ Thu, 27 Feb 2014, Team SNAP! @ Thu, 31 Mar 2016, ShanMan @ Thu, 30 May 2013, PDV @ Fri, 26 Feb 2016, C @ Thu, 29 Aug 2013, Captain Squelch @ Thu, 27 Aug 2015, Four Balls @ Thu, 28 May 2015, C# @ Thu, 29 Aug 2013, One Point @ Thu, 29 Aug 2013, Hung Like David Foster Wallace @ Thu, 12 Dec 2013, Tits McGee @ Thu, 12 Dec 2013, Candy Cane @ Thu, 12 Dec 2013, Sandstorm @ Thu, 30 Jan 2014, We'll Tell You A Name Later @ Thu, 30 Jan 2014, Not As Good As Clojure @ Thu, 29 Oct 2015
3. Largest prime factor C# @ Thu, 29 Aug 2013, Persona 4 @ Thu, 30 Oct 2014, Fudge Bar @ Thu, 27 Jun 2013, North West @ Thu, 27 Jun 2013, Ruby Slippers @ Thu, 01 Aug 2013, Not As Good As Clojure @ Thu, 29 Oct 2015, Dragon Fruit @ Mon, 29 Apr 2013, Chicken Burritos @ Thu, 27 Jun 2013, Tits McGee @ Thu, 12 Dec 2013
4. Largest palindrome product Angry Armadillos @ Fri, 30 Jan 2015, Tits McGee @ Thu, 12 Dec 2013, Chicken Burritos @ Thu, 27 Jun 2013, Kepler @ Thu, 30 May 2013, North West @ Thu, 27 Jun 2013, Persona 4 @ Thu, 30 Oct 2014, 99 Problems @ Mon, 29 Apr 2013
5. Smallest multiple Team Beer @ Thu, 28 Aug 2014, Sandstorm @ Thu, 30 Jan 2014, Higi @ Mon, 29 Apr 2013, Strawberry Sample @ Thu, 29 May 2014, Tits McGee @ Thu, 12 Dec 2013, Bears @ Thu, 29 Aug 2013, NASA @ Thu, 02 Apr 2015, max(pow(e,r)) @ Thu, 28 Aug 2014, North West @ Thu, 27 Jun 2013
6. Sum square difference We'll Tell You A Name Later @ Thu, 30 Jan 2014, Team This Table @ Thu, 28 Aug 2014, max(pow(e,r)) @ Thu, 28 Aug 2014, Sandstorm @ Thu, 30 Jan 2014, Persona 4 @ Thu, 30 Oct 2014, 99 Problems @ Mon, 29 Apr 2013, C @ Thu, 29 Aug 2013, Team Awesome @ Thu, 28 Aug 2014, Prime Triplets @ Thu, 11 May 2017, North West @ Thu, 27 Jun 2013, Tits McGee @ Thu, 12 Dec 2013, Team Beer @ Thu, 28 Aug 2014
7. 10001st prime The Julii @ Thu, 28 May 2015, Higi @ Mon, 29 Apr 2013, Team Beer @ Thu, 28 Aug 2014, Angry Armadillos @ Fri, 30 Jan 2015, No Ether @ Thurs, 26 Feb 2015, Swift @ Fri, 26 Feb 2016, North West @ Thu, 27 Jun 2013, Team This Table @ Thu, 28 Aug 2014, Vegetarian Kernel Sanders @ Thu, 31 Jul 2014
8. Largest product in a series Team This Table @ Thu, 28 Aug 2014, North West @ Thu, 27 Jun 2013, Tits McGee @ Thu, 12 Dec 2013, Team f.lux @ Thu, 27 Oct 2016, C++ @ Thu, 29 Aug 2013
9. Special Pythagorean triplet Oiler @ Thu, 30 Jan 2014, Team 🐍 @ Thu, 27 Oct 2016
10. Summation of primes Tits McGee @ Thu, 12 Dec 2013, Team This Table @ Thu, 28 Aug 2014, Mighty Morphin' Power Angers @ Fri, 30 Jan 2015, Retro Secret Agents @ Thu, 30 Jan 2014, The Square Roots @ Fri, 30 Jan 2015, Vegetarian Kernel Sanders @ Thu, 31 Jul 2014, Mountain Dew @ Thu, 29 May 2014, North West @ Thu, 27 Jun 2013, Swift @ Fri, 26 Feb 2016, Angry Armadillos @ Fri, 30 Jan 2015, We'll Tell You A Name Later @ Thu, 30 Jan 2014
11. Largest product in a grid Team Huy @ Thu, 25 Jun 2015, North West @ Thu, 27 Jun 2013, Precise Pangolin @ Thu, 29 May 2014
12. Highly divisible triangular number Secret 🐿++ @ Thu, 29 Jun 2017
13. Large sum North West @ Thu, 27 Jun 2013, Team Awesome @ Thu, 28 Aug 2014, AtomicAwesomePants @ Thu, 25 Sep 2014, Team Beer @ Thu, 28 Aug 2014, Secret 🐿++ @ Thu, 29 Jun 2017, Team Bernie @ Thu, 31 Jul 2014, nerdBusters @ Wed, 19 Nov 2014
14. Longest Collatz sequence Team Awesome @ Thu, 28 Aug 2014, C++ @ Thu, 26 Sep 2013, Strawberry Sample @ Thu, 29 May 2014, North West @ Thu, 27 Jun 2013
15. Lattice paths Programmers Just Want To Have Fun @ Thu, 30 Apr 2015, Back from Seoul @ Thu, 01 May 2014, Chuckles @ Thu, 27 Aug 2015, Prime Triplets @ Thu, 11 May 2017
16. Power digit sum 99 Problems @ Mon, 29 Apr 2013, AwesomeSauceChicken @ Thu, 25 Sep 2014, Team Beer @ Thu, 28 Aug 2014, The Square Roots @ Fri, 30 Jan 2015, Oiler @ Thu, 30 Jan 2014, Team Bernie @ Thu, 31 Jul 2014
17. Number letter counts Hot Sauce @ Thu, 30 Jan 2014, 99 Problems @ Mon, 29 Apr 2013, Secret Squirrel @ Thu, 01 Sep 2016
18. Maximum path sum I Vegetarian Kernel Sanders @ Thu, 31 Jul 2014, Project Humbug @ Thu, 12 Dec 2013
19. Counting Sundays Diablo @ Thu, 27 Feb 2014, Joshua @ Thu, 29 May 2014, Awesome Monster @ Thu, 01 May 2014
20. Factorial digit sum 99 Problems @ Mon, 29 Apr 2013, I got %d problems but a %s ain't one @ Thu, 01 May 2014, Ghostbusters @ Fri, 30 Jan 2015, Mighty Morphin' Power Angers @ Fri, 30 Jan 2015, Team Bernie @ Thu, 31 Jul 2014, Kepler @ Thu, 30 May 2013, Awesome Monster @ Thu, 01 May 2014, Oiler @ Thu, 30 Jan 2014, Programmers Just Want To Have Fun @ Thu, 30 Apr 2015, Team Beer @ Thu, 28 Aug 2014, Team Awesome @ Thu, 28 Aug 2014
21. Amicable numbers U of I @ Thu, 01 Aug 2013, No Ether @ Thurs, 26 Feb 2015, Project Humbug @ Thu, 12 Dec 2013, The 43ers @ Thu, 28 Jan 2016, Tits McGee @ Thu, 12 Dec 2013, Programmers Just Want To Have Fun @ Thu, 30 Apr 2015, The 26ers @ Thu, 28 Jul 2016
22. Names scores We'll Tell You A Name Later @ Thu, 30 Jan 2014, Vegetarian Kernel Sanders @ Thu, 31 Jul 2014, Team Bernie @ Thu, 31 Jul 2014, Started From The Bottom @ Fri, 30 Jan 2015
23. Non-abundant sums Vegetarian Kernel Sanders @ Thu, 31 Jul 2014
24. Lexicographic permutations Team Awesome @ Thu, 28 Aug 2014
25. 1000-digit Fibonacci number Oiler @ Thu, 30 Jan 2014, The Steves @ Thu, 30 Jan 2014, Kitten Sprinkles @ Thu, 27 Aug 2015, 99 Problems @ Mon, 29 Apr 2013, Nameless @ Thu, 31 Jul 2014, Awesome Monster @ Thu, 01 May 2014, The Unknowns @ Thu, 26 May 2016, Chicken Burritos @ Thu, 27 Jun 2013, Diablo @ Thu, 27 Feb 2014, Secret 🐿 @ Wed, 28 Sep 2016, Kepler @ Thu, 30 May 2013, Team Awesome @ Thu, 28 Aug 2014, North West @ Thu, 27 Jun 2013
26. Reciprocal cycles The 26ers @ Thu, 28 Jul 2016
27. Quadratic primes 🍝🍝🍝 @ Wed, 28 Sep 2016
28. Number spiral diagonals SubjectiveC @ Thu, 25 Sep 2014
29. Distinct powers Chicken Burritos @ Thu, 27 Jun 2013, Awesome Monster @ Thu, 01 May 2014
30. Digit fifth powers 99 Problems @ Mon, 29 Apr 2013, Team Bernie @ Thu, 31 Jul 2014, C++ @ Thu, 29 Aug 2013, 3 @ Thu, 27 Mar 2014, Chicken Burritos @ Thu, 27 Jun 2013
31. Coin sums Kepler @ Thu, 30 May 2013, Chicken Burritos @ Thu, 27 Jun 2013, Vegetarian Kernel Sanders @ Thu, 31 Jul 2014
32. Pandigital products
33. Digit canceling fractions Secret 🐿 @ Thu, 26 Jan 2017
34. Digit factorials C++ @ Thu, 29 Aug 2013, Chicken Burritos @ Thu, 27 Jun 2013, Oiler @ Thu, 30 Jan 2014, Team Awesome @ Thu, 28 Aug 2014, AtomicAwesomePants @ Thu, 25 Sep 2014, C++ @ Thu, 26 Sep 2013
35. Circular primes Team This Table @ Thu, 28 Aug 2014
36. Double-base palindromes Team Awesome @ Thu, 28 Aug 2014, I got %d problems but a %s ain't one @ Thu, 01 May 2014, SubjectiveC @ Thu, 25 Sep 2014
37. Truncatable primes Veggiecadres @ Wed, 19 Nov 2014, SubjectiveC @ Thu, 25 Sep 2014
38. Pandigital multiples SubjectiveC @ Thu, 25 Sep 2014
39. Integer right triangles Project Humbug @ Thu, 12 Dec 2013
40. Champernowne's constant Spencer @ Thu, 28 Jul 2016
41. Pandigital prime Spencer @ Thu, 28 Jul 2016
42. Coded triangle numbers Chuckles @ Thu, 27 Aug 2015, Spencer @ Thu, 28 Jul 2016
43. Sub-string divisibility The 43ers @ Thu, 28 Jan 2016
44. Pentagon numbers Nameless @ Thu, 31 Jul 2014
45. Triangular, pentagonal, and hexagonal Secret 🐿 @ Thu, 27 Oct 2016
46. Goldbach's other conjecture Chicken Burritos @ Thu, 27 Jun 2013
47. Distinct primes factors C++ @ Thu, 29 Aug 2013, ℚ² @ Thu, 29 Jun 2017
48. Self powers Team This Table @ Thu, 28 Aug 2014, Honeybadger Don't Care @ Thu, 29 May 2014, I got %d problems but a %s ain't one @ Thu, 01 May 2014, Ghostbusters @ Fri, 30 Jan 2015, Mighty Morphin' Power Angers @ Fri, 30 Jan 2015, 3 @ Thu, 27 Mar 2014, Oiler @ Thu, 30 Jan 2014, AtomicAwesomePants @ Thu, 25 Sep 2014, North West @ Thu, 27 Jun 2013, Chicken Burritos @ Thu, 27 Jun 2013, 99 Problems @ Mon, 29 Apr 2013, The Square Roots @ Fri, 30 Jan 2015, Fünke @ Thu, 30 May 2013, Awesome Monster @ Thu, 01 May 2014
49. Prime permutations Hung Like David Foster Wallace @ Thu, 12 Dec 2013, 3 @ Thu, 27 Mar 2014, Higi @ Mon, 29 Apr 2013, Team This Table @ Thu, 28 Aug 2014
50. Consecutive prime sum Project Humbug @ Thu, 12 Dec 2013, Team This Table @ Thu, 28 Aug 2014, Chicken Burritos @ Thu, 27 Jun 2013
51. Prime digit replacements
52. Permuted multiples Higi @ Mon, 29 Apr 2013, Oiler @ Thu, 30 Jan 2014, Team This Table @ Thu, 28 Aug 2014, The Steves @ Thu, 30 Jan 2014, Back from Seoul @ Thu, 01 May 2014, 3 @ Thu, 27 Mar 2014
53. Combinatoric selections The Chargers @ Thu, 15 Jun 2017, Back from Seoul @ Thu, 01 May 2014, Project Humbug @ Thu, 12 Dec 2013, Just For Fun @ Mon, 29 Apr 2013, Kitten Sprinkles @ Thu, 27 Aug 2015, Oiler @ Thu, 30 Jan 2014
54. Poker hands
55. Lychrel numbers The Chargers @ Thu, 15 Jun 2017, 1 2 3 4 @ Thu, 30 May 2013
56. Powerful digit sum Nameless @ Thu, 31 Jul 2014, We Hate Primes @ Thu, 27 Mar 2014, AwesomeSauceChicken @ Thu, 25 Sep 2014, Oiler @ Thu, 30 Jan 2014
57. Square root convergents
58. Spiral primes
59. XOR decryption Fünke @ Thu, 30 May 2013, Secret 🐿 @ Thu, 27 Oct 2016
60. Prime pair sets
61. Cyclical figurate numbers
62. Cubic permutations The Chargers @ Thu, 15 Jun 2017
63. Powerful digit counts
64. Odd period square roots
65. Convergents of e
66. Diophantine equation
67. Maximum path sum II Vegetarian Kernel Sanders @ Thu, 31 Jul 2014, Honeybadger Don't Care @ Thu, 29 May 2014, Just For Fun @ Mon, 29 Apr 2013, Project Humbug @ Thu, 12 Dec 2013, Mighty Morphin' Power Angers @ Fri, 30 Jan 2015
68. Magic 5-gon ring
69. Totient maximum Lone Prime @ Thu, 15 Jun 2017, Infinite Sadness @ Thu, 30 Apr 2015
70. Totient permutation
71. Ordered fractions
72. Counting fractions
73. Counting fractions in a range
74. Digit factorial chains
75. Singular integer right triangles
76. Counting summations
77. Prime summations
78. Coin partitions
79. Passcode derivation Fünke @ Thu, 30 May 2013, Team 🐍 @ Thu, 27 Oct 2016
80. Square root digital expansion
81. Path sum: two ways Awesome Monster @ Thu, 01 May 2014, Emerald Vipers @ Thu, 30 Apr 2015
82. Path sum: three ways Mountain Dew @ Thu, 29 May 2014
83. Path sum: four ways
84. Monopoly odds
85. Counting rectangles Awesome Monster @ Thu, 01 May 2014
86. Cuboid route
87. Prime power triples 0^0 @ Thu, 25 May 2017, Oiler @ Thu, 30 Jan 2014
88. Product-sum numbers
89. Roman numerals 🍝🍝🍝 @ Wed, 28 Sep 2016
90. Cube digit pairs
91. Right triangles with integer coordinates
92. Square digit chains Lone Prime @ Thu, 15 Jun 2017, We Hate Primes @ Thu, 27 Mar 2014, Kepler @ Thu, 30 May 2013, AtomicAwesomePants @ Thu, 25 Sep 2014, AwesomeSauceChicken @ Thu, 25 Sep 2014
93. Arithmetic expressions
94. Almost equilateral triangles
95. Amicable chains Lone Prime @ Thu, 15 Jun 2017
96. Su Doku
97. Large non-Mersenne prime AwesomeSauceChicken @ Thu, 25 Sep 2014, Fünke @ Thu, 30 May 2013, Username @ Thu, 30 May 2013, Squirrels @ Thu, 02 Apr 2015, Kepler @ Thu, 30 May 2013, Angry Armadillos @ Fri, 30 Jan 2015, Fabulous Five @ Thu, 27 Jul 2017
98. Anagramic squares The Redshirts @ Thu, 30 Oct 2014
99. Largest exponential
100. Arranged probability
101. Optimum polynomial
102. Triangle containment CII @ Thu, 30 Mar 2017
103. Special subset sums: optimum
104. Pandigital Fibonacci ends
105. Special subset sums: testing
106. Special subset sums: meta-testing
107. Minimal network
108. Diophantine reciprocals I
109. Darts
110. Diophantine reciprocals II
111. Primes with runs
112. Bouncy numbers Team Danny @ Thu, 28 Aug 2014, Angry Armadillos @ Fri, 30 Jan 2015, AwesomeSauceChicken @ Thu, 25 Sep 2014, Better Than Clojure @ Thu, 29 Oct 2015, Three Minutes @ Thu, 27 Apr 2017, Secret 🐿 @ Thu, 11 May 2017, HashBit @ Thu, 31 Mar 2016, Infinite Sadness @ Thu, 30 Apr 2015, 99 Problems @ Mon, 29 Apr 2013
113. Non-bouncy numbers
114. Counting block combinations I Just Add One! @ Thu, 01 Sep 2016
115. Counting block combinations II
116. Red, green or blue tiles
117. Red, green, and blue tiles
118. Pandigital prime sets
119. Digit power sum
120. Square remainders No @ Thu, 25 May 2017, max(pow(e,r)) @ Thu, 28 Aug 2014, ℚ² @ Thu, 29 Jun 2017
121. Disc game prize fund
122. Efficient exponentiation
123. Prime square remainders
124. Ordered radicals
125. Palindromic sums Team Beer @ Thu, 28 Aug 2014
126. Cuboid layers
127. abc-hits
128. Hexagonal tile differences
129. Repunit divisibility
130. Composites with prime repunit property
131. Prime cube partnership
132. Large repunit factors
133. Repunit nonfactors
134. Prime pair connection
135. Same differences
136. Singleton difference
137. Fibonacci golden nuggets
138. Special isosceles triangles
139. Pythagorean tiles
140. Modified Fibonacci golden nuggets
141. Investigating progressive numbers, n, which are also square.
142. Perfect Square Collection
143. Investigating the Torricelli point of a triangle
144. Investigating multiple reflections of a laser beam.
145. How many reversible numbers are there below one-billion? Codew @ Thu, 27 Jul 2017
146. Investigating a Prime Pattern
147. Rectangles in cross-hatched grids
148. Exploring Pascal's triangle. Sierpiński’s 🧀 @ Thu, 26 Jan 2017
149. Searching for a maximum-sum subsequence.
150. Searching a triangular array for a sub-triangle having minimum-sum.
151. Paper sheets of standard sizes: an expected-value problem.
152. Writing 1/2 as a sum of inverse squares
153. Investigating Gaussian Integers
154. Exploring Pascal's pyramid.
155. Counting Capacitor Circuits.
156. Counting Digits
157. Solving the diophantine equation 1/a+1/b= p/10n
158. Exploring strings for which only one character comes lexicographically after its neighbour to the left. 👨‍💻 @ Thu, 23 Feb 2017
159. Digital root sums of factorisations.
160. Factorial trailing digits
161. Triominoes
162. Hexadecimal numbers
163. Cross-hatched triangles
164. Numbers for which no three consecutive digits have a sum greater than a given value.
165. Intersections
166. Criss Cross
167. Investigating Ulam sequences
168. Number Rotations
169. Exploring the number of different ways a number can be expressed as a sum of powers of 2.
170. Find the largest 0 to 9 pandigital that can be formed by concatenating products.
171. Finding numbers for which the sum of the squares of the digits is a square.
172. Investigating numbers with few repeated digits.
173. Using up to one million tiles how many different 'hollow' square laminae can be formed? Pier Revue @ Thu, 27 Apr 2017
174. Counting the number of 'hollow' square laminae that can form one, two, three, ... distinct arrangements.
175. Fractions involving the number of different ways a number can be expressed as a sum of powers of 2.
176. Right-angled triangles that share a cathetus.
177. Integer angled Quadrilaterals.
178. Step Numbers
179. Consecutive positive divisors Prime Triplets @ Thu, 11 May 2017, MAD @ Fri, 26 Feb 2016
180. Rational zeros of a function of three variables.
181. Investigating in how many ways objects of two different colours can be grouped.
182. RSA encryption
183. Maximum product of parts
184. Triangles containing the origin.
185. Number Mind
186. Connectedness of a network.
187. Semiprimes Cauliflower @ Thu, 28 Jul 2016
188. The hyperexponentiation of a number
189. Tri-colouring a triangular grid
190. Maximising a weighted product
191. Prize Strings Young Diagram @ Thu, 28 Jan 2016
192. Best Approximations
193. Squarefree Numbers
194. Coloured Configurations
195. Inscribed circles of triangles with one angle of 60 degrees
196. Prime triplets
197. Investigating the behaviour of a recursively defined sequence
198. Ambiguous Numbers
199. Iterative Circle Packing
200. Find the 200th prime-proof sqube containing the contiguous sub-string '200'
201. Subsets with a unique sum
202. Laserbeam
203. Squarefree Binomial Coefficients
204. Generalised Hamming Numbers
205. Dice Game Programmers Just Want To Have Fun @ Thu, 30 Apr 2015, AbstractSolutionFactorie @ Thu, 26 May 2016, Team 🐍 @ Thu, 27 Oct 2016, Awesome @ Thu, 02 Apr 2015
206. Concealed Square Squirrels @ Thu, 02 Apr 2015, AtomicAwesomePants @ Thu, 25 Sep 2014, Sierpiński’s 🧀 @ Thu, 27 Jul 2017, Angry Armadillos @ Fri, 30 Jan 2015, AwesomeSauceChicken @ Thu, 25 Sep 2014, Awesome @ Thu, 02 Apr 2015, DynamicDuo @ Wed, 19 Nov 2014, Team Beer @ Thu, 28 Aug 2014
207. Integer partition equations
208. Robot Walks
209. Circular Logic
210. Obtuse Angled Triangles
211. Divisor Square Sum
212. Combined Volume of Cuboids
213. Flea Circus
214. Totient Chains
215. Crack-free Walls
216. Investigating the primality of numbers of the form 2n2-1
217. Balanced Numbers
218. Perfect right-angled triangles
219. Skew-cost coding
220. Heighway Dragon
221. Alexandrian Integers
222. Sphere Packing
223. Almost right-angled triangles I
224. Almost right-angled triangles II
225. Tribonacci non-divisors
226. A Scoop of Blancmange
227. The Chase
228. Minkowski Sums
229. Four Representations using Squares
230. Fibonacci Words
231. The prime factorisation of binomial coefficients
232. The Race
233. Lattice points on a circle
234. Semidivisible numbers
235. An Arithmetic Geometric sequence
236. Luxury Hampers
237. Tours on a 4 x n playing board
238. Infinite string tour
239. Twenty-two Foolish Primes
240. Top Dice
241. Perfection Quotients
242. Odd Triplets
243. Resilience Pier Revue @ Thu, 27 Apr 2017
244. Sliders
245. Coresilience
246. Tangents to an ellipse
247. Squares under a hyperbola
248. Numbers for which Euler’s totient function equals 13!
249. Prime Subset Sums
250. 250250
251. Cardano Triplets
252. Convex Holes
253. Tidying up
254. Sums of Digit Factorials
255. Rounded Square Roots
256. Tatami-Free Rooms
257. Angular Bisectors
258. A lagged Fibonacci sequence
259. Reachable Numbers
260. Stone Game
261. Pivotal Square Sums
262. Mountain Range.
263. An engineers' dream come true
264. Triangle Centres
265. Binary Circles
266. Pseudo Square Root
267. Billionaire
268. Counting numbers with at least four distinct prime factors less than 100
269. Polynomials with at least one integer root
270. Cutting Squares
271. Modular Cubes, part 1
272. Modular Cubes, part 2
273. Sum of Squares
274. Divisibility Multipliers
275. Balanced Sculptures
276. Primitive Triangles
277. A Modified Collatz sequence
278. Linear Combinations of Semiprimes
279. Triangles with integral sides and an integral angle
280. Ant and seeds
281. Pizza Toppings
282. The Ackermann function
283. Integer sided triangles for which the area/perimeter ratio is integral.
284. Steady Squares
285. Pythagorean odds
286. Scoring probabilities
287. Quadtree encoding (a simple compression algorithm)
288. An enormous factorial
289. Eulerian Cycles
290. Digital Signature
291. Panaitopol Primes
292. Pythagorean Polygons
293. Pseudo-Fortunate Numbers
294. Sum of digits - experience #23
295. Lenticular holes
296. Angular Bisector and Tangent
297. Zeckendorf Representation
298. Selective Amnesia
299. Three similar triangles
300. Protein folding
301. Nim Young Diagram @ Thu, 28 Jan 2016
302. Strong Achilles Numbers
303. Multiples with small digits
304. Primonacci
305. Reflexive Position
306. Paper-strip Game
307. Chip Defects
308. An amazing Prime-generating Automaton
309. Integer Ladders
310. Nim Square
311. Biclinic Integral Quadrilaterals
312. Cyclic paths on Sierpiński graphs
313. Sliding game
314. The Mouse on the Moon
315. Digital root clocks
316. Numbers in decimal expansions
317. Firecracker
318. 2011 nines
319. Bounded Sequences
320. Factorials divisible by a huge integer
321. Swapping Counters
322. Binomial coefficients divisible by 10
323. Bitwise-OR operations on random integers Fabulous Five @ Thu, 27 Jul 2017, Sierpiński’s 🧀 @ Thu, 27 Jul 2017
324. Building a tower
325. Stone Game II
326. Modulo Summations
327. Rooms of Doom
328. Lowest-cost Search
329. Prime Frog
330. Euler's Number
331. Cross flips
332. Spherical triangles
333. Special partitions
334. Spilling the beans
335. Gathering the beans
336. Maximix Arrangements
337. Totient Stairstep Sequences
338. Cutting Rectangular Grid Paper
339. Peredur fab Efrawg
340. Crazy Function
341. Golomb's self-describing sequence
342. The totient of a square is a cube
343. Fractional Sequences
344. Silver dollar game
345. Matrix Sum Coca-Cola® @ Thu, 25 May 2017
346. Strong Repunits
347. Largest integer divisible by two primes
348. Sum of a square and a cube
349. Langton's ant
350. Constraining the least greatest and the greatest least
351. Hexagonal orchards
352. Blood tests
353. Risky moon
354. Distances in a bee's honeycomb
355. Maximal coprime subset
356. Largest roots of cubic polynomials
357. Prime generating integers No Ether @ Thurs, 26 Feb 2015
358. Cyclic numbers
359. Hilbert's New Hotel
360. Scary Sphere
361. Subsequence of Thue-Morse sequence
362. Squarefree factors
363. Bézier Curves
364. Comfortable distance
365. A huge binomial coefficient
366. Stone Game III
367. bozo sort
368. A Kempner-like series
369. Badugi
370. Geometric triangles
371. Licence plates
372. Pencils of rays
373. Circumscribed Circles
374. Maximum Integer Partition Product
375. Minimum of subsequences
376. Nontransitive sets of dice
377. Sum of digits, experience 13
378. Triangle Triples
379. Least common multiple count
380. Amazing Mazes!
381. (prime-k) factorial
382. Generating polygons
383. Divisibility comparison between factorials
384. Rudin-Shapiro sequence
385. Ellipses inside triangles
386. Maximum length of an antichain
387. Harshad Numbers The PinPals @ Thu, 25 Jun 2015
388. Distinct Lines
389. Platonic Dice
390. Triangles with non rational sides and integral area
391. Hopping Game
392. Enmeshed unit circle
393. Migrating ants
394. Eating pie
395. Pythagorean tree
396. Weak Goodstein sequence
397. Triangle on parabola
398. Cutting rope
399. Squarefree Fibonacci Numbers
400. Fibonacci tree game
401. Sum of squares of divisors
402. Integer-valued polynomials
403. Lattice points enclosed by parabola and line
404. Crisscross Ellipses
405. A rectangular tiling
406. Guessing Game
407. Idempotents
408. Admissible paths through a grid
409. Nim Extreme
410. Circle and tangent line
411. Uphill paths
412. Gnomon numbering
413. One-child Numbers
414. Kaprekar constant
415. Titanic sets
416. A frog's trip
417. Reciprocal cycles II
418. Factorisation triples
419. Look and say sequence
420. 2x2 positive integer matrix
421. Prime factors of n15+1
422. Sequence of points on a hyperbola
423. Consecutive die throws
424. Kakuro
425. Prime connection
426. Box-ball system
427. n-sequences
428. Necklace of circles