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 A369600 #12 Jan 27 2024 10:31:17
%S A369600 1,3,12,56,291,1638,9780,60948,391821,2577575,17256918,117150228,
%T A369600 804343302,5575177026,38957753136,274143594685,1941037464402,
%U A369600 13818185220783,98848503602394,710185896393792,5122358166219855,37076879861508830,269235792063692580
%N A369600 Expansion of (1/x) * Series_Reversion( x * (1/(1+x)^3 - x^3) ).
%H A369600 <a href="/index/Res#revert">Index entries for reversions of series</a>
%F A369600 a(n) = (1/(n+1)) * Sum_{k=0..floor(n/3)} binomial(n+k,k) * binomial(3*n+3*k+3,n-3*k).
%o A369600 (PARI) my(N=30, x='x+O('x^N)); Vec(serreverse(x*(1/(1+x)^3-x^3))/x)
%o A369600 (PARI) a(n) = sum(k=0, n\3, binomial(n+k, k)*binomial(3*n+3*k+3, n-3*k))/(n+1);
%Y A369600 Cf. A198888, A369599.
%Y A369600 Cf. A274379, A274735.
%K A369600 nonn
%O A369600 0,2
%A A369600 _Seiichi Manyama_, Jan 27 2024