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 A368972 #16 Jan 13 2024 10:45:33
%S A368972 1,3,15,88,564,3819,26851,194025,1431498,10735548,81580008,626697786,
%T A368972 4858272450,37954323885,298487957670,2361025981335,18770449480056,
%U A368972 149897172319290,1201831832357041,9670416882346848,78062823843714528,631988009034161246
%N A368972 Expansion of (1/x) * Series_Reversion( x * (1-x+x^3)^3 ).
%C A368972 a(702) is negative.
%H A368972 Seiichi Manyama, <a href="/A368972/b368972.txt">Table of n, a(n) for n = 0..1000</a>
%H A368972 <a href="/index/Res#revert">Index entries for reversions of series</a>
%F A368972 a(n) = (1/(n+1)) * Sum_{k=0..floor(n/3)} (-1)^k * binomial(3*n+k+2,k) * binomial(4*n-2*k+2,n-3*k).
%o A368972 (PARI) my(N=30, x='x+O('x^N)); Vec(serreverse(x*(1-x+x^3)^3)/x)
%o A368972 (PARI) a(n, s=3, 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 A368972 Cf. A368964.
%K A368972 sign
%O A368972 0,2
%A A368972 _Seiichi Manyama_, Jan 10 2024