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 A369231 #12 Jan 17 2024 09:35:37
%S A369231 1,1,2,7,26,98,385,1569,6556,27908,120624,528030,2336202,10430155,
%T A369231 46930285,212597901,968833424,4438398734,20428750419,94424634294,
%U A369231 438104297376,2039690282940,9526029685218,44617396906698,209526541600978,986339358246758,4653571637230839
%N A369231 Expansion of (1/x) * Series_Reversion( x * (1-x)^3 / (1-x+x^3)^2 ).
%H A369231 <a href="/index/Res#revert">Index entries for reversions of series</a>
%F A369231 a(n) = (1/(n+1)) * Sum_{k=0..floor(n/3)} binomial(2*n+2,k) * binomial(2*n-2*k,n-3*k).
%o A369231 (PARI) my(N=30, x='x+O('x^N)); Vec(serreverse(x*(1-x)^3/(1-x+x^3)^2)/x)
%o A369231 (PARI) a(n, s=3, t=2, u=3) = sum(k=0, n\s, binomial(t*(n+1), k)*binomial((u-t+1)*(n+1)-(s-1)*k-2, n-s*k))/(n+1);
%Y A369231 Cf. A366052, A369232.
%Y A369231 Cf. A369229.
%K A369231 nonn
%O A369231 0,3
%A A369231 _Seiichi Manyama_, Jan 17 2024