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 A103317 #16 Feb 16 2025 08:32:56 %S A103317 3,7,379,6917,208003 %N A103317 Primes p such that p! - 1 is also prime. %C A103317 The members are the primes in A002982 (n! - 1 is prime). %D A103317 R. K. Guy, Unsolved Problems in Number Theory, Section A2. %H A103317 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/FactorialPrime.html">Factorial Prime</a> %H A103317 <a href="/index/Fa#factorial">Index entries for sequences related to factorial numbers.</a> %e A103317 3 is prime and 3! - 1 = 5 is prime, so 3 is a member. %t A103317 Select[Prime[Range[100]], PrimeQ[#! - 1] &] (* _Vladimir Joseph Stephan Orlovsky_, Feb 01 2012 *) %o A103317 (PARI) isok(n) = ispseudoprime(n) && ispseudoprime(n!-1); \\ _Jinyuan Wang_, Jan 20 2020 %Y A103317 Cf. A002982, A093804. %K A103317 nonn,hard,more %O A103317 1,1 %A A103317 _Jonathan Sondow_, Jan 31 2005 %E A103317 a(5)=208003 (found on Jul 27 2016, by Sou Fukui), added by _Jinyuan Wang_, Jan 20 2020