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 A380603 #8 Jan 28 2025 08:38:32
%S A380603 1,2,12,140,2512,61392,1905184,71781824,3183563520,162497556224,
%T A380603 9383803201024,604888546242048,43056560538093568,3354362248463544320,
%U A380603 283895464602180231168,25938521255822517813248,2544584391277895815069696,266765818037212169468706816,29764238411096397030375424000
%N A380603 Expansion of e.g.f. exp(2*x*G(x)^2) where G(x) = 1 + x*G(x)^3 is the g.f. of A001764.
%F A380603 E.g.f.: B(x)^2, where B(x) is the e.g.f. of A380511.
%F A380603 a(n) = 2 * n! * Sum_{k=0..n-1} 2^(n-k) * binomial(2*n+k,k)/((2*n+k) * (n-k-1)!) for n > 0.
%o A380603 (PARI) a(n) = if(n==0, 1, 2*n!*sum(k=0, n-1, 2^(n-k)*binomial(2*n+k, k)/((2*n+k)*(n-k-1)!)));
%Y A380603 Cf. A001764, A251573, A380511.
%K A380603 nonn
%O A380603 0,2
%A A380603 _Seiichi Manyama_, Jan 28 2025