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 A245716 #11 Jul 30 2014 20:25:58 %S A245716 0,0,0,1,2,1,0,0,2,0,3,1,3,0,2,0,3,1,0,0,2,0,3,0,3,0,0,0,4,1,0,0,0,0, %T A245716 3,0,3,0,2,0,0,1,4,0,2,0,3,0,0,0,0,0,3,0,4,0,0,0,0,1,0,0,0,0,3,0,3,0, %U A245716 2,0,0,1,3,0,0,0,3,0,0,0,2,0,4,0,4,0,0,0,0,0,0,0,0,0,3,0,0,0,2,0,0,1,3,0,2,0,3,1,0,0,2,0,4,0,0,0,0,0,0,0 %N A245716 Least number k > 0 such that n + k! and n - k! are both prime, or 0 if no such k exists. %C A245716 For a(n) > 0, a(n)! < n for all n. Thus a(n) = 0 is definite. %H A245716 Jens Kruse Andersen, <a href="/A245716/b245716.txt">Table of n, a(n) for n = 1..10000</a> %e A245716 13 + 1! and 13 - 1! are not both prime. %e A245716 13 + 2! and 13 - 2! are not both prime. %e A245716 13 + 3! and 13 - 3! are both prime (19 and 7). Thus a(13) = 3. %o A245716 (PARI) %o A245716 a(n)=for(k=1,n,if(ispseudoprime(n-k!)&&ispseudoprime(n+k!),return(k))) %o A245716 vector(150,n,a(n)) %Y A245716 Cf. A245714, A245715. %K A245716 nonn %O A245716 1,5 %A A245716 _Derek Orr_, Jul 30 2014