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 A301423 #19 Jan 15 2023 02:07:59 %S A301423 4,5,6,11,15,44,66,168,575,1713 %N A301423 Numbers k such that !k/(k-1) is prime, where !k = A000166(k) is the subfactorial of k. %C A301423 Also numbers k such that A000255(k-2) is prime. %C A301423 The corresponding primes are 3, 11, 53, 1468457, 34361893981, 22742406079421034331584846001936724930824184898296683, ... %C A301423 a(11) > 35000. - _Robert Price_, Apr 14 2018 %t A301423 Select[Range[2,100], PrimeQ[Subfactorial[#]/(#-1)] &] %o A301423 (PARI) isok(n) = (n != 1) && isprime(n!*sum(k=0, n, (-1)^k/k!)/(n-1)); \\ _Michel Marcus_, Mar 24 2018 %Y A301423 Cf. A000166, A000255. %K A301423 nonn,more %O A301423 1,1 %A A301423 _Amiram Eldar_, Mar 20 2018