ID

Title Solved by Difficulty
1Multiples of 3 or 59686305%
2Even Fibonacci numbers7727305%
3Largest prime factor5560695%
6Sum square difference4985645%
5Smallest multiple4955495%
4Largest palindrome product4921785%
710001st prime4268585%
9Special Pythagorean triplet3628535%
8Largest product in a series3578055%
10Summation of primes3325775%
11Largest product in a grid2389085%
16Power digit sum2333035%
14Longest Collatz sequence2310755%
13Large sum2308015%
12Highly divisible triangular number2254935%
20Factorial digit sum2020105%
15Lattice paths1907485%
251000-digit Fibonacci number1586375%
17Number letter counts1548375%
21Amicable numbers1495385%
18Maximum path sum I1482315%
19Counting Sundays1377205%
22Names scores1375315%
24Lexicographic permutations1172855%
48Self powers1143375%
30Digit fifth powers1124825%
28Number spiral diagonals1104595%
29Distinct powers1078855%
23Non-abundant sums1067425%
67Maximum path sum II977075%
34Digit factorials963755%
36Double-base palindromes908055%
27Quadratic primes895435%
31Coin sums871775%
35Circular primes866425%
26Reciprocal cycles860895%
40Champernowne's constant819355%
42Coded triangle numbers760925%
37Truncatable primes753155%
39Integer right triangles749425%
33Digit cancelling fractions734685%
32Pandigital products730725%
45Triangular, pentagonal, and hexagonal725505%
41Pandigital prime697535%
52Permuted multiples666235%
38Pandigital multiples645915%
50Consecutive prime sum639275%
46Goldbach's other conjecture631395%
43Sub-string divisibility613455%
53Combinatoric selections602205%
44Pentagon numbers600095%
56Powerful digit sum594275%
47Distinct primes factors594195%
49Prime permutations593165%
55Lychrel numbers550125%
63Powerful digit counts441735%
97Large non-Mersenne prime439215%
57Square root convergents426415%
92Square digit chains423515%
59XOR decryption421955%
79Passcode derivation417385%
58Spiral primes411925%
206Concealed Square246625%
686Powers of Two29625%
700Eulercoin26625%
719Number Splitting25665%
684Inverse Digit Sum23205%
751Concatenation Coincidence15505%
54Poker hands3700010%
69Totient maximum3563310%
81Path sum: two ways3496710%
99Largest exponential3114710%
71Ordered fractions2995110%
76Counting summations2915210%
357Prime generating integers811910%
387Harshad Numbers468010%
650Divisors of Binomial Product153510%
757Stealthy Numbers83210%
745Sum of Squares II82510%
51Prime digit replacements3481215%
62Cubic permutations3224115%
65Convergents of e3057015%
74Digit factorial chains2734015%
73Counting fractions in a range2556615%
85Counting rectangles2518015%
112Bouncy numbers2498915%
102Triangle containment2234315%
345Matrix Sum565715%
347Largest integer divisible by two primes455015%
346Strong Repunits430815%
381(prime-k) factorial419615%
500Problem 500!!!394315%
549Divisibility of factorials265515%
622Riffle Shuffles166115%
694Cube-full Divisors85615%
749Near Power Sums54115%
60Prime pair sets2741120%
61Cyclical figurate numbers2615320%
72Counting fractions2285620%
70Totient permutation2278820%
64Odd period square roots2268320%
89Roman numerals2156920%
82Path sum: three ways2152620%
87Prime power triples2131020%
80Square root digital expansion2024920%
145How many reversible numbers are there below one-billion?1682720%
429Sum of squares of unitary divisors249520%
407Idempotents241120%
601Divisibility streaks196620%
5165-smooth totients153520%
618Numbers with a given prime factor sum98520%
668Square root smooth Numbers96120%
609π sequences89220%
659Largest prime84720%
704Factors of Two in Binomial Coefficients78720%
688Piles of Plates67220%
754Product of Gauss Factorials52020%
68Magic 5-gon ring2125525%
66Diophantine equation2015125%
77Prime summations1957725%
83Path sum: four ways1850925%
75Singular integer right triangles1839925%
96Su Doku1749625%
104Pandigital Fibonacci ends1642925%
120Square remainders1396625%
124Ordered radicals1387025%
125Palindromic sums1367925%
179Consecutive positive divisors1128925%
187Semiprimes1122325%
203Squarefree Binomial Coefficients917225%
348Sum of a square and a cube301225%
401Sum of squares of divisors252425%
512Sums of totients of powers146025%
425Prime connection143125%
479Roots on the Rise126325%
531Chinese leftovers109725%
571Super Pandigital Numbers106725%
6752^{\omega(n)}67425%
752Powers of 1+\sqrt 751025%
78Coin partitions1725530%
100Arranged probability1657630%
95Amicable chains1457630%
108Diophantine reciprocals I1280230%
119Digit power sum1253030%
123Prime square remainders1165630%
173Using up to one million tiles how many different "hollow" square laminae can be formed?911930%
204Generalised Hamming Numbers732730%
293Pseudo-Fortunate Numbers295230%
451Modular inverses139430%
485Maximum number of divisors112730%
443GCD sequence110630%
435Polynomials of Fibonacci numbers109130%
58147-smooth triangular numbers81930%
784Reciprocal Pairs28430%
94Almost equilateral triangles1258835%
93Arithmetic expressions1202835%
98Anagramic squares1160335%
243Resilience954935%
191Prize Strings708335%
188The hyperexponentiation of a number639135%
303Multiples with small digits360335%
277A Modified Collatz sequence321735%
349Langton's ant190035%
288An enormous factorial163335%
343Fractional Sequences139135%
463A weird recurrence relation106235%
417Reciprocal cycles II83835%
565Divisibility of sum of divisors59035%
625Gcd sum56435%
621Expressing an integer as the sum of triangular numbers53035%
545Faulhaber's Formulas51035%
110Diophantine reciprocals II816740%
131Prime cube partnership741040%
174Counting the number of "hollow" square laminae that can form one, two, three, ... distinct arrangements585240%
231The prime factorisation of binomial coefficients543640%
214Totient Chains519440%
235An Arithmetic Geometric sequence498640%
207Integer partition equations470740%
304Primonacci214240%
365A huge binomial coefficient122940%
487Sums of power sums62740%
634Numbers of the form a^2b^357340%
748Upside down Diophantine equation26840%
111Primes with runs730345%
134Prime pair connection704845%
118Pandigital prime sets701845%
135Same differences641545%
132Large repunit factors636345%
129Repunit divisibility631945%
130Composites with prime repunit property593845%
138Special isosceles triangles584745%
142Perfect Square Collection583145%
197Investigating the behaviour of a recursively defined sequence488845%
183Maximum product of parts466145%
225Tribonacci non-divisors444345%
216Investigating the primality of numbers of the form 2n2-1405845%
291Panaitopol Primes142045%
642Sum of largest prime factors33545%
127abc-hits626550%
136Singleton difference568750%
133Repunit nonfactors554350%
137Fibonacci golden nuggets553950%
146Investigating a Prime Pattern 505950%
169Exploring the number of different ways a number can be expressed as a sum of powers of 2504550%
211Divisor Square Sum416050%
320Factorials divisible by a huge integer84950%
521Smallest prime factor71550%
708Twos are all you need28250%
140Modified Fibonacci golden nuggets434355%
193Squarefree Numbers331355%
678Fermat-like Equations22155%
160Factorial trailing digits348660%
182RSA encryption258960%
271Modular Cubes, part 1234660%
196Prime triplets255565%
221Alexandrian Integers205265%
273Sum of Squares136070%
248Numbers for which Euler’s totient function equals 13!128370%
379Least common multiple count50570%
192Best Approximations158375%
795Alternating GCD Sum195-