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 A216043 #15 Feb 14 2021 18:34:13
%S A216043 1,4,12,105,112,322,8807,8831
%N A216043 Numbers k such that Sum_{j=1..k-1} (2j)!/3^j is an integer.
%C A216043 Next term > 2000000.
%t A216043 seq={}; sum=0; fak=1; k=0; While[k<10000, sum+=fak; If[Denominator[sum]==1, AppendTo[seq,k+1]]; k++; fak*=2*k*(2k-1)/3;]; seq
%Y A216043 Cf. A215972, A216042, A216044, A216045
%K A216043 nonn,more
%O A216043 1,2
%A A216043 _Vaclav Kotesovec_, Aug 30 2012