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 A366239 #9 Oct 05 2023 08:34:54
%S A366239 1,2,8,49,329,2401,18452,147140,1206157,10101011,86047138,743288984,
%T A366239 6495476548,57321239999,510104531479,4572492374150,41247768216331,
%U A366239 374175606700172,3411195598361653,31236732721224722,287182875831208468,2649838553953071239
%N A366239 G.f. A(x) satisfies A(x) = 1 + x + x*(1 + x)^2*A(x)^3.
%F A366239 a(n) = Sum_{k=0..n} binomial(4*k+1,n-k) * binomial(3*k,k)/(2*k+1).
%o A366239 (PARI) a(n) = sum(k=0, n, binomial(4*k+1, n-k)*binomial(3*k, k)/(2*k+1));
%Y A366239 Cf. A364336, A366240, A366241.
%Y A366239 Cf. A366221.
%K A366239 nonn
%O A366239 0,2
%A A366239 _Seiichi Manyama_, Oct 05 2023