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 A366556 #10 Oct 14 2023 14:00:00
%S A366556 1,1,0,0,1,3,3,1,3,15,30,30,27,87,252,420,475,747,2064,4632,7203,9933,
%T A366556 19635,47025,92013,144745,237510,498498,1073817,1969131,3267411,
%U A366556 5977881,12462579,25035747,45090936,79414344,153115299,311198457,600883569,1090988379,2012793705
%N A366556 G.f. A(x) satisfies A(x) = 1 + x + x^4*A(x)^3.
%F A366556 a(n) = Sum_{k=0..floor(n/4)} binomial(2*k+1,n-4*k) * binomial(3*k,k)/(2*k+1).
%F A366556 a(n) = A366592(n) + A366592(n-1).
%o A366556 (PARI) a(n) = sum(k=0, n\4, binomial(2*k+1, n-4*k)*binomial(3*k, k)/(2*k+1));
%Y A366556 Cf. A019497, A366266, A366555.
%Y A366556 Cf. A366554, A366558.
%Y A366556 Cf. A366592.
%K A366556 nonn
%O A366556 0,6
%A A366556 _Seiichi Manyama_, Oct 13 2023