ID NAME QUALITY USERS ACC % DIFFICULTY C I
30691 Ada and Diary   16
5151 Alice’s Cube   6 412
27
24
10232 Distinct Primes   36 3358
9
8
4556 Think I will Buy Me a Football Team   15 1729
8
14
5451 Not So Flat After All   6 1004
12
8
13753 Amazing Prime Sequence   30 2227
10
12
30826 Bernoulli numbers   2 3
17
17
31066 Number Breaking   2 65
12
12
21357 Crucial Equation   31 2275
3
11
3505 Prime Number Theorem   12 1105
13
15
9032 Cube Free Numbers   29 2736
14
12
526 Divisors   16 1051
17
15
530 Divisors 2   4 627
15
17
22403 Divisors of factorial   40 928
15
14
74 Divisor Summation   47 10932
7
9
23963 Easy Factorials   8 63
26
26
4141 Euler Totient Function   63 5903
8
12
22382 Euler Totient Function Depth   13 167
12
12
4942 Integer Factorization (15 digits)   17 1704
11
9
25584 Factorial Modulo   16 263
8
12
25067 Fibonacci Polynomial   4 53
23
23
5970 Finding Primes   13 808
17
15
6264 Rank of a Fraction   1 105
9
34
5978 Frequent Prime Ranges   4 532
4
4
3871 GCD Extreme   26 701
19
27
26045 GCD OF MATRIX (hard)   1 6
12005 Grass Planting   3 110
38
17
18202 HUGE GCD   5 359
5
13
4164 A conjecture of Paul Erdős   2 510
1
9
12241 Classification from Erdős and Selfridge   15
27195 Find The Number   4 123
14
11
6221 Increasing Powers of K   283
34
42
6256 Inversion Count   248 8516
15
17
12183 Help the Commander in Chief   16 302
14
16
3442 The last digit   76 15052
9
9
5971 LCM Sum   25 1224
19
31
9385 Strictly not a Prime   3 276
21
14
6450 PP numbers   3 697
17
17
3932 Point Connection Game in a Circle   1 603
17
26
12933 n-divisors   36 1350
18
17
6556 N DIV PHI_N   4 543
4
30
8238 N-Factorful   35 1350
17
16
6285 Another Game With Numbers   14 708
11
13
28561 Number of divisors   1 19
3107 Odd Numbers of Divisors   9 662
17
17
4839 Ant   2 172
26
34
5732 Paradox   19 846
16
18
3591 Patting Heads   2 493
11
11
134 Phony Primes   1 169
26
26
24689 Fibo and non fibo   10 231
18
18

#number-theory

The problem involves number theory, a branch of pure mathematics

https://en.wikipedia.org/wiki/Number_theory http://mathworld.wolfram.com/NumberTheory.html http://www.math.brown.edu/~jhs/frintch1ch6.pdf http://www.britannica.com/topic/number-theory