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 A366590 #10 Oct 14 2023 13:20:20
%S A366590 1,0,1,2,4,12,30,84,238,680,1993,5882,17575,52976,160870,491924,
%T A366590 1512940,4677672,14529744,45320640,141897039,445792908,1404899598,
%U A366590 4440113940,14069493813,44689897200,142268117566,453839997836,1450547245960,4644492976232,14896047099592
%N A366590 G.f. A(x) satisfies A(x) = 1 + x^2*(1+x)^2*A(x)^3.
%F A366590 a(n) = Sum_{k=0..floor(n/2)} binomial(2*k,n-2*k) * binomial(3*k,k)/(2*k+1).
%o A366590 (PARI) a(n) = sum(k=0, n\2, binomial(2*k, n-2*k)*binomial(3*k, k)/(2*k+1));
%Y A366590 Cf. A366221, A366591, A366592.
%Y A366590 Cf. A019497.
%K A366590 nonn
%O A366590 0,4
%A A366590 _Seiichi Manyama_, Oct 14 2023