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 A364645 #15 Aug 02 2023 09:38:58
%S A364645 1,2,3,6,19,51,114,312,981,2616,6564,19647,59922,159056,430302,
%T A364645 1329996,3926217,10498968,30052851,93244764,267690168,729649143,
%U A364645 2173840338,6663260223,18768583674,52570016676,160362713250,481809941520,1346473504182,3886164785178
%N A364645 G.f. satisfies A(x) = 1/(1 - 3*x) - x*A(x)^3.
%H A364645 Seiichi Manyama, <a href="/A364645/b364645.txt">Table of n, a(n) for n = 0..1000</a>
%F A364645 a(n) = Sum_{k=0..n} (-1)^k * 3^(n-k) * binomial(n+k,2*k) * binomial(3*k,k) / (2*k+1).
%o A364645 (PARI) a(n) = sum(k=0, n, (-1)^k*3^(n-k)*binomial(n+k, 2*k)*binomial(3*k, k)/(2*k+1));
%Y A364645 Cf. A364641, A364646, A364647.
%Y A364645 Cf. A005773, A349254, A349256, A349534.
%K A364645 nonn
%O A364645 0,2
%A A364645 _Seiichi Manyama_, Jul 31 2023