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 A369487 #10 Jan 24 2024 08:00:20
%S A369487 1,2,10,57,365,2492,17797,131290,992704,7652558,59918667,475213662,
%T A369487 3809620760,30820493162,251309225465,2063207320841,17040385542611,
%U A369487 141487339935740,1180337222858348,9888553030497869,83160409524964381,701782096849536054
%N A369487 Expansion of (1/x) * Series_Reversion( x / (1-x) * (1-x-x^2)^3 ).
%H A369487 <a href="/index/Res#revert">Index entries for reversions of series</a>
%F A369487 a(n) = (1/(n+1)) * Sum_{k=0..floor(n/2)} binomial(3*n+k+2,k) * binomial(3*n-k+1,n-2*k).
%o A369487 (PARI) my(N=30, x='x+O('x^N)); Vec(serreverse(x/(1-x)*(1-x-x^2)^3)/x)
%o A369487 (PARI) a(n, s=2, t=3, u=1) = sum(k=0, n\s, binomial(t*(n+1)+k-1, k)*binomial((t-u+1)*(n+1)-(s-1)*k-2, n-s*k))/(n+1);
%Y A369487 Cf. A369488.
%K A369487 nonn
%O A369487 0,2
%A A369487 _Seiichi Manyama_, Jan 24 2024