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 A245715 #10 Jul 30 2014 20:25:39 %S A245715 0,0,1,1,2,1,2,1,2,0,3,1,2,1,2,0,3,1,2,1,2,0,3,1,2,4,4,0,3,1,2,1,2,0, %T A245715 3,0,3,1,2,0,4,1,2,1,2,0,3,1,2,0,0,0,3,1,2,0,0,0,3,1,2,1,2,0,3,0,3,1, %U A245715 2,0,4,1,2,1,2,0,3,0,3,1,2,0,4,1,2,0,0,0,3,1,2,0,0,0,3,0,4,1,2,0,0,1,2,1,2,0,3,1,2,1,2,0,3,1,2,0,0,0,3 %N A245715 Least number k > 0 such that n - k! is prime, or 0 if no such k exists. %C A245715 a(n)! < n for all n. Thus a(n) = 0 is definite. %H A245715 Jens Kruse Andersen, <a href="/A245715/b245715.txt">Table of n, a(n) for n = 1..10000</a> %e A245715 11 - 1! = 10 is not prime. %e A245715 11 - 2! = 9 is not prime. %e A245715 11 - 3! = 5 is prime. Thus a(11) = 3. %o A245715 (PARI) %o A245715 a(n)=for(k=1,n,if(ispseudoprime(n-k!),return(k))) %o A245715 vector(150,n,a(n)) %K A245715 nonn %O A245715 1,5 %A A245715 _Derek Orr_, Jul 30 2014