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 A373683 #9 Jun 13 2024 08:15:53
%S A373683 1,1,3,13,61,441,3031,28813,267513,3088081,36278731,491262861,
%T A373683 6962025973,108395586313,1791145742751,31601369155021,594291393830641,
%U A373683 11740929829286433,246910933786777363,5406641472165854221,125497950720670828461,3018786042678264770521
%N A373683 Expansion of e.g.f. exp(x / (1 - x^2)) / (1 - x^2).
%F A373683 a(n) = n! * Sum_{k=0..floor(n/2)} binomial(n-k,k)/(n-2*k)!.
%F A373683 a(n) == 1 (mod 2).
%o A373683 (PARI) a(n) = n!*sum(k=0, n\2, binomial(n-k, k)/(n-2*k)!);
%Y A373683 Cf. A373681, A373682.
%Y A373683 Cf. A088009.
%K A373683 nonn
%O A373683 0,3
%A A373683 _Seiichi Manyama_, Jun 13 2024