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 A368971 #13 Jan 13 2024 10:45:37
%S A368971 1,3,12,52,228,969,3795,12285,19227,-162316,-2334219,-20233746,
%T A368971 -146642814,-956899038,-5761740810,-32172133140,-164988072288,
%U A368971 -752632536117,-2777949390584,-5070274066512,41416739288496,663038498204040,6188361199762260,47738255512890555
%N A368971 Expansion of (1/x) * Series_Reversion( x * (1-x+x^2)^3 ).
%H A368971 Seiichi Manyama, <a href="/A368971/b368971.txt">Table of n, a(n) for n = 0..1000</a>
%H A368971 <a href="/index/Res#revert">Index entries for reversions of series</a>
%F A368971 a(n) = (1/(n+1)) * Sum_{k=0..floor(n/2)} (-1)^k * binomial(3*n+k+2,k) * binomial(4*n-k+2,n-2*k).
%o A368971 (PARI) my(N=30, x='x+O('x^N)); Vec(serreverse(x*(1-x+x^2)^3)/x)
%o A368971 (PARI) a(n, s=2, t=3, 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 A368971 Cf. A368963.
%K A368971 sign
%O A368971 0,2
%A A368971 _Seiichi Manyama_, Jan 10 2024