This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A152220 #15 Jun 10 2025 01:31:35
%S A152220 11,31,107,571,971,4931
%N A152220 Primes p such that p^2 divides m!-1 for some integer m < p.
%C A152220 For numbers k such that k! - 1 is divisible by a square see A152219.
%C A152220 a(7) > 60000, if it exists. - _Amiram Eldar_, Oct 23 2024
%t A152220 aa = {}; Do[If[(Sqrt[n! - 1] /. Sqrt[_] -> 1) > 1, Print[(Sqrt[n! - 1] /. Sqrt[_] -> 1)]; AppendTo[aa, (Sqrt[n! - 1] /. Sqrt[_] -> 1)]], {n, 1, 1000}]; aa
%t A152220 q[p_] := Module[{m = 2}, While[m < p && ! Divisible[m! - 1, p^2], m++]; Divisible[m! - 1, p^2]]; Select[Prime[Range[660]], q] (* _Amiram Eldar_, Oct 23 2024 *)
%o A152220 (PARI) is(p) = if(isprime(p), my(m = 2); while(m < p && (m! - 1) % (p^2), m++); !((m! - 1) % (p^2)), 0); \\ _Amiram Eldar_, Oct 23 2024
%Y A152220 Cf. A064237, A152219, A152231, A152232.
%K A152220 nonn,more,hard
%O A152220 1,1
%A A152220 _Artur Jasinski_, Nov 29 2008
%E A152220 a(6) from _Artur Jasinski_, Nov 30 2008