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 A369594 #6 Jan 27 2024 10:31:25
%S A369594 1,3,12,58,318,1887,11772,75969,502554,3389056,23211312,161015058,
%T A369594 1128976523,7988381001,56968671948,409046328954,2954644519365,
%U A369594 21455293440345,156534285598068,1146881543952792,8434926025730955,62250461094154372,460859182211975184
%N A369594 Expansion of (1/x) * Series_Reversion( x / ((1+x)^3 * (1+x^3)^3) ).
%H A369594 <a href="/index/Res#revert">Index entries for reversions of series</a>
%F A369594 a(n) = (1/(n+1)) * Sum_{k=0..floor(n/3)} binomial(3*n+3,k) * binomial(3*n+3,n-3*k).
%o A369594 (PARI) my(N=30, x='x+O('x^N)); Vec(serreverse(x/((1+x)^3*(1+x^3)^3))/x)
%o A369594 (PARI) a(n, s=3, t=3, u=3) = sum(k=0, n\s, binomial(t*(n+1), k)*binomial(u*(n+1), n-s*k))/(n+1);
%Y A369594 Cf. A369441.
%K A369594 nonn
%O A369594 0,2
%A A369594 _Seiichi Manyama_, Jan 27 2024