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 A380606 #8 Jan 28 2025 08:38:25
%S A380606 1,3,27,459,11817,411183,18090459,963856071,60351513777,4344290172891,
%T A380606 353515902334299,32093341598006307,3215888732193019353,
%U A380606 352572962113533923271,41981774097966848444763,5395346708265250105968927,744369113570455426540767201,109733083289828610273889269939
%N A380606 Expansion of e.g.f. exp(3*x*G(x)^3) where G(x) = 1 + x*G(x)^4 is the g.f. of A002293.
%F A380606 E.g.f.: B(x)^3, where B(x) is the e.g.f. of A380515.
%F A380606 a(n) = 3 * n! * Sum_{k=0..n-1} 3^(n-k) * binomial(3*n+k,k)/((3*n+k) * (n-k-1)!) for n > 0.
%o A380606 (PARI) a(n) = if(n==0, 1, 3*n!*sum(k=0, n-1, 3^(n-k)*binomial(3*n+k, k)/((3*n+k)*(n-k-1)!)));
%Y A380606 Cf. A002293, A251574, A380515, A380605.
%K A380606 nonn
%O A380606 0,2
%A A380606 _Seiichi Manyama_, Jan 28 2025