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 A064392 #6 Dec 15 2017 17:35:39 %S A064392 1,2,5,10,13,26,37,65,74,130,185,370,463,481,926,962,2315,2405,4630, %T A064392 4810,6019,12038,17131,30095,34262,60190,85655,171310,222703 %N A064392 Numbers in A064383 that are squarefree. %o A064392 (PARI) for(n=1,10^6,x=sum(k=0,n,(-1)^k*k!); if(Mod(x,n)==0 && issquarefree(n),print(n))) %K A064392 more,nonn %O A064392 1,2 %A A064392 _Jason Earls_, Sep 28 2001 %E A064392 a(17)-a(29) from _Donovan Johnson_, Nov 30 2008