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 A373681 #9 Jun 13 2024 08:15:57
%S A373681 1,1,3,19,85,861,6391,74383,822249,10724185,156044971,2331428331,
%T A373681 40840033213,706624333429,14138302767135,281981427966631,
%U A373681 6273491346471121,142296558637593393,3475950835899954259,88235303457193306435,2351639524607386287141
%N A373681 Expansion of e.g.f. exp(x / (1 - x^2)^2) / (1 - x^2).
%F A373681 a(n) = n! * Sum_{k=0..floor(n/2)} binomial(2*n-3*k,k)/(n-2*k)!.
%F A373681 a(n) == 1 (mod 2).
%o A373681 (PARI) a(n) = n!*sum(k=0, n\2, binomial(2*n-3*k, k)/(n-2*k)!);
%Y A373681 Cf. A373682, A373683.
%Y A373681 Cf. A373620.
%K A373681 nonn
%O A373681 0,3
%A A373681 _Seiichi Manyama_, Jun 13 2024