21567

Appears in sequences

• Number of ways to partition n elements into pie slices of different sizes.at n=34A032153
• a(1) = 9, then the smallest number such that the forward as well as the reverse n-th partial concatenation is a prime for n>1. (Reverse concatenation is taken term-wise and not digit-wise).at n=43A083995
• a(n) = smallest number greater than a(n-1) having a largest proper divisor that is greater than and coprime to a(n-1); a(1) = 1.at n=36A098144
• Numbers k such that k^2 divides 22^k-1.at n=9A128402
• a(n) = 49*n^2 - 2*n.at n=20A157362
• Numbers k such that k^3 divides 17^(k^2) + 1.at n=22A177817
• a(n) = 7*n*(2*n + 1).at n=39A195026
• 27-gonal numbers: a(n) = n*(25*n-23)/2.at n=42A255186
• Numbers n such that n^2 divides (17^n + 1).at n=15A292392
• Numbers m such that there are precisely 19 groups of order m.at n=11A298910
• Replacing each digit d in decimal expansion of n with d^2 yields a prime at each step when done recursively three times.at n=25A316604