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 A371387 #8 Mar 21 2024 09:19:34
%S A371387 1,11,205,4647,116873,3135635,87924597,2545845135,75534363601,
%T A371387 2284439539035,70166186106333,2182759455876663,68630655620066265,
%U A371387 2177561996773904483,69632831106680348165,2241852665024904670239,72608750028928583936673
%N A371387 Expansion of (1/x) * Series_Reversion( x * (1-4*x)^3 / (1-x) ).
%H A371387 <a href="/index/Res#revert">Index entries for reversions of series</a>
%F A371387 a(n) = (1/(n+1)) * Sum_{k=0..n} 3^k * binomial(3*n+k+2,k) * binomial(3*n+1,n-k).
%o A371387 (PARI) my(N=20, x='x+O('x^N)); Vec(serreverse(x*(1-4*x)^3/(1-x))/x)
%o A371387 (PARI) a(n) = sum(k=0, n, 3^k*binomial(3*n+k+2, k)*binomial(3*n+1, n-k))/(n+1);
%Y A371387 Cf. A131763, A371386.
%Y A371387 Cf. A371365.
%K A371387 nonn
%O A371387 0,2
%A A371387 _Seiichi Manyama_, Mar 20 2024