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 A239412 #42 Aug 12 2016 03:09:26 %S A239412 4,6,8,16,18,92,254,258,660,1850,2496,2774,2832,7430,28540,32124 %N A239412 Numbers n such that (n!-k)/(n-k) is prime for some k. %C A239412 a(14) > 3000. %C A239412 There is only one value of k that can work, and it is n/2. Thus, all members of the sequence are even. %C A239412 Even numbers n such that 2*(n-1)!-1 is prime. %C A239412 (Odd members of A076133) + 1. - _Robert Israel_, Aug 11 2016 %e A239412 (4!-k)/(4-k) is prime for some k (namely, k = 2). Thus, 4 is a member of this sequence. %p A239412 select(t -> isprime(2*(t-1)!-1), [seq(q,q=2..1000, 2)]); # _Robert Israel_, Aug 11 2016 %t A239412 Select[Range[2, 10^3, 2], PrimeQ[2 (# - 1)! - 1] &] (* _Michael De Vlieger_, Aug 11 2016 *) %o A239412 (PARI) a(n)=for(k=1,int(n/2),s=(n!-k)/(n-k);if(floor(s)==s,if(ispseudoprime(s),return(k)))) %o A239412 n=1;while(n<1000,if(a(n),print1(n,", "));n+=1) %Y A239412 Cf. A076133. %K A239412 nonn,hard,more %O A239412 1,1 %A A239412 _Derek Orr_, May 26 2014 %E A239412 Edited and a(14)-a(16) added by _Robert Israel_, Aug 11 2016