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 A215990 #8 Jul 02 2017 20:23:12
%S A215990 0,1,1,7,13,7,73,461,1721,7391,35741,95833,140902,7208291,6221977,
%T A215990 738064507,5846167507,49265043007,440034922507,4152348777757,
%U A215990 41275487330257,431068442131507,4718790944945257,27013799863651691,322866652557800441,502628413904332477
%N A215990 Numerator of sum( k!/2^k, k=1..n ).
%C A215990 If a(n) is even, then A215976(n)=0 (and n is listed in A215974); the converse is not necessarily true.
%t A215990 Table[Numerator[Sum[k!/2^k,{k,n}]],{n,0,30}] (* _Harvey P. Dale_, Jul 02 2017 *)
%o A215990 (PARI) a(n)=numerator(sum(k=1,n,k!/2^k))
%o A215990 (PARI) s=0;for(k=1,29,print1(numerator(s+=k!/2^k),","))
%K A215990 nonn
%O A215990 0,4
%A A215990 _M. F. Hasler_, Aug 29 2012