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 A368454 #8 Dec 25 2023 09:59:25
%S A368454 1,0,3,12,93,840,9183,117012,1704153,27921360,508302363,10178888412,
%T A368454 222365364213,5262547606680,134124963385143,3662574088282212,
%U A368454 106682195378484273,3301614846549616800,108189336403552025523,3742170760095124874412
%N A368454 Expansion of e.g.f. 2*exp(-x) / (3 - exp(2*x)).
%F A368454 a(n) = (-1)^n + Sum_{k=1..n} 2^(k-1) * binomial(n,k) * a(n-k).
%o A368454 (PARI) a_vector(n) = my(v=vector(n+1)); for(i=0, n, v[i+1]=(-1)^i+sum(j=1, i, 2^(j-1)*binomial(i, j)*v[i-j+1])); v;
%Y A368454 Cf. A367977, A368442, A368443.
%K A368454 nonn
%O A368454 0,3
%A A368454 _Seiichi Manyama_, Dec 24 2023