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 A380605 #8 Jan 28 2025 08:38:29
%S A380605 1,2,16,260,6544,224672,9797824,518778752,32332764160,2319086302208,
%T A380605 188178044545024,17043816700333568,1704575787500099584,
%U A380605 186577340672207974400,22185432394552519868416,2847773562263558405439488,392481896442656581445287936,57805399208817471918851883008
%N A380605 Expansion of e.g.f. exp(2*x*G(x)^3) where G(x) = 1 + x*G(x)^4 is the g.f. of A002293.
%F A380605 E.g.f.: B(x)^2, where B(x) is the e.g.f. of A380515.
%F A380605 a(n) = 3 * n! * Sum_{k=0..n-1} 2^(n-k) * binomial(3*n+k,k)/((3*n+k) * (n-k-1)!) for n > 0.
%o A380605 (PARI) a(n) = if(n==0, 1, 3*n!*sum(k=0, n-1, 2^(n-k)*binomial(3*n+k, k)/((3*n+k)*(n-k-1)!)));
%Y A380605 Cf. A002293, A251574, A380515, A380606.
%K A380605 nonn
%O A380605 0,2
%A A380605 _Seiichi Manyama_, Jan 28 2025