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 A368969 #13 Jan 13 2024 10:46:02
%S A368969 1,2,5,12,22,0,-284,-1938,-9367,-36938,-118105,-260130,56637,4890560,
%T A368969 35945616,186674620,782890326,2632462236,5987222046,-2241224328,
%U A368969 -129137211280,-967479390360,-5145272296080,-22060975744080,-75535676951124,-172915138783080
%N A368969 Expansion of (1/x) * Series_Reversion( x * (1-x+x^2)^2 ).
%H A368969 Seiichi Manyama, <a href="/A368969/b368969.txt">Table of n, a(n) for n = 0..1000</a>
%H A368969 <a href="/index/Res#revert">Index entries for reversions of series</a>
%F A368969 a(n) = (1/(n+1)) * Sum_{k=0..floor(n/2)} (-1)^k * binomial(2*n+k+1,k) * binomial(3*n-k+1,n-2*k).
%o A368969 (PARI) my(N=30, x='x+O('x^N)); Vec(serreverse(x*(1-x+x^2)^2)/x)
%o A368969 (PARI) a(n, s=2, t=2, u=0) = sum(k=0, n\s, (-1)^k*binomial(t*(n+1)+k-1, k)*binomial((t+u+1)*(n+1)-(s-1)*k-2, n-s*k))/(n+1);
%Y A368969 Cf. A368973, A368975.
%Y A368969 Cf. A368961.
%K A368969 sign
%O A368969 0,2
%A A368969 _Seiichi Manyama_, Jan 10 2024