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 A319224 #55 Apr 18 2025 13:02:03 %S A319224 7,11,19,61,2557 %N A319224 Integers q for which f(q) = ((((q - 2)! - 1) / q) - 1) / (q + 1) is a prime number. %C A319224 For q < 7, f(q) is not an integer. %C A319224 f(q) for q = 2557 is a PRP7592. %C A319224 According to Wilson's theorem, f(q) can be an integer only if q is prime. %C A319224 a(6) > 30000. - _Michael S. Branicky_, Apr 18 2025 %t A319224 a[q_]:=If[PrimeQ[((((q - 2)! - 1) / q) - 1) / (q + 1)], q]; DeleteCases[Array[a, 100], Null] (* _Stefano Spezia_, Nov 04 2018 *) %o A319224 (PARI) forprime(q=7, 2557, my(p = ((((q - 2)! - 1) / q) - 1) / (q + 1)); if(ispseudoprime(p), print1(q, ", "))) %Y A319224 Cf. A193447, A319304. %K A319224 nonn,hard,more %O A319224 1,1 %A A319224 _Rashid Naimi_, Sep 13 2018