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 A369484 #11 Jan 24 2024 05:57:16
%S A369484 1,3,12,57,301,1700,10045,61303,383335,2443113,15811317,103627692,
%T A369484 686402602,4587643765,30900426417,209539509967,1429344492215,
%U A369484 9801262309209,67523359213569,467136798336153,3243948604314619,22604271635042853,158001453530915361
%N A369484 Expansion of (1/x) * Series_Reversion( x / ((1+x) * (1+x+x^3)^2) ).
%H A369484 <a href="/index/Res#revert">Index entries for reversions of series</a>
%F A369484 a(n) = (1/(n+1)) * Sum_{k=0..floor(n/3)} binomial(2*n+2,k) * binomial(3*n-k+3,n-3*k).
%o A369484 (PARI) my(N=30, x='x+O('x^N)); Vec(serreverse(x/((1+x)*(1+x+x^3)^2))/x)
%o A369484 (PARI) a(n, s=3, t=2, u=1) = sum(k=0, n\s, binomial(t*(n+1), k)*binomial((t+u)*(n+1)-k, n-s*k))/(n+1);
%Y A369484 Cf. A369483, A369485.
%K A369484 nonn
%O A369484 0,2
%A A369484 _Seiichi Manyama_, Jan 23 2024