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 A368439 #9 Dec 25 2023 10:02:15
%S A368439 1,7,97,2023,56257,1955527,81570337,3969606823,220777431937,
%T A368439 13813838801287,960354511044577,73441487204670823,6126887497334519617,
%U A368439 553733062241471461447,53894653951229272883617,5620230710788836168938023,625160202763025501303191297
%N A368439 Expansion of e.g.f. exp(x) / (4 - 3*exp(2*x)).
%F A368439 a(n) = 1 + 3 * Sum_{k=1..n} 2^k * binomial(n,k) * a(n-k).
%o A368439 (PARI) a_vector(n) = my(v=vector(n+1)); for(i=0, n, v[i+1]=1+3*sum(j=1, i, 2^j*binomial(i, j)*v[i-j+1])); v;
%Y A368439 Cf. A080253, A337026, A368438.
%K A368439 nonn
%O A368439 0,2
%A A368439 _Seiichi Manyama_, Dec 24 2023