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 A366555 #11 Oct 14 2023 13:59:49
%S A366555 1,1,0,1,3,3,4,15,30,42,99,255,475,915,2232,4977,9945,21945,51093,
%T A366555 110634,238005,542341,1227390,2696841,6035886,13770402,31001133,
%U A366555 69485295,157945293,359888373,814699002,1850816823,4231092060,9659302380,22028018679
%N A366555 G.f. A(x) satisfies A(x) = 1 + x + x^3*A(x)^3.
%F A366555 a(n) = Sum_{k=0..floor(n/3)} binomial(2*k+1,n-3*k) * binomial(3*k,k)/(2*k+1).
%F A366555 a(n) = A366591(n) + A366591(n-1).
%o A366555 (PARI) a(n) = sum(k=0, n\3, binomial(2*k+1, n-3*k)*binomial(3*k, k)/(2*k+1));
%Y A366555 Cf. A019497, A366266, A366556.
%Y A366555 Cf. A366591.
%K A366555 nonn
%O A366555 0,5
%A A366555 _Seiichi Manyama_, Oct 13 2023