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 A371365 #11 Mar 20 2024 09:39:32
%S A371365 1,9,141,2701,57513,1307553,31083925,763267077,19208408721,
%T A371365 492817411705,12842067417309,338956669920189,9042967461581753,
%U A371365 243464712274093713,6606427290991922277,180492205687604057013,4960765361688213527073
%N A371365 Expansion of (1/x) * Series_Reversion( x * (1-4*x)^3 / (1-3*x) ).
%H A371365 <a href="/index/Res#revert">Index entries for reversions of series</a>
%F A371365 a(n) = (1/(n+1)) * Sum_{k=0..n} 3^(n-k) * binomial(3*n+k+2,k) * binomial(3*n+1,n-k).
%o A371365 (PARI) my(N=20, x='x+O('x^N)); Vec(serreverse(x*(1-4*x)^3/(1-3*x))/x)
%o A371365 (PARI) a(n) = sum(k=0, n, 3^(n-k)*binomial(3*n+k+2, k)*binomial(3*n+1, n-k))/(n+1);
%Y A371365 Cf. A059231, A371364.
%Y A371365 Cf. A369023, A371363.
%K A371365 nonn
%O A371365 0,2
%A A371365 _Seiichi Manyama_, Mar 19 2024