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 A237443 #32 Dec 21 2024 23:52:46 %S A237443 1,2,7,13,23,5666,32918 %N A237443 Numbers m such that (2m)! - m! + 1 is prime. %C A237443 If it exists, a(7) > 7*10^3. - _Michal Paulovic_, Feb 17 2024 %C A237443 If it exists, a(8) > 6*10^4. - _Kellen Shenton_, Dec 21 2024 %e A237443 2 is in the sequence because 4! - 2! + 1 = 23 is prime. %e A237443 7 is in the sequence because 14! - 7! + 1 = 87178286161 is prime. %e A237443 12 is not in the sequence because 24! - 12! + 1 = 620448401733238960358401 = 587 * 21523 * 49109415278124401. %t A237443 Select[Range[100], PrimeQ[(2#)! - #! + 1] &] (* _Alonso del Arte_, Feb 09 2014 *) %o A237443 (PARI) for(n = 1, 2500, if(isprime((2*n)! - n! + 1), print1(n, ", "))) %Y A237443 Cf. A118812 (corresponding primes). %K A237443 nonn,hard,more %O A237443 1,2 %A A237443 _Rick L. Shepherd_, Feb 07 2014 %E A237443 a(6) from _Michal Paulovic_, Nov 22 2023 %E A237443 a(7) from _Kellen Shenton_, Dec 21 2024