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 A366116 #9 Sep 30 2023 13:09:26
%S A366116 1,1,1,0,-3,-9,-15,-7,50,203,429,382,-1045,-5845,-14751,-18627,20255,
%T A366116 184818,549630,879632,-156085,-6025489,-21267251,-40911195,-17629620,
%U A366116 193929269,835617523,1881543582,1674869775,-5855762293,-32848801375,-85601962056,-108647926359
%N A366116 Expansion of (1/x) * Series_Reversion( x*(1+x+x^3)/(1+x)^2 ).
%F A366116 a(n) = (1/(n+1)) * Sum_{k=0..floor(n/3)} (-1)^k * binomial(n+k,k) * binomial(n-k+1,n-3*k).
%o A366116 (PARI) a(n) = sum(k=0, n\3, (-1)^k*binomial(n+k, k)*binomial(n-k+1, n-3*k))/(n+1);
%Y A366116 Cf. A366117, A366118, A366119.
%Y A366116 Cf. A366095.
%K A366116 sign
%O A366116 0,5
%A A366116 _Seiichi Manyama_, Sep 29 2023