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 A366097 #8 Sep 29 2023 10:04:38
%S A366097 1,3,12,56,287,1564,8896,52217,313955,1923775,11970066,75427608,
%T A366097 480365740,3086989128,19992893796,130363352003,855099212950,
%U A366097 5638480905533,37354602517624,248515024509486,1659620048332369,11121368629141886,74759777174598964
%N A366097 Expansion of (1/x) * Series_Reversion( x*(1+x-x^3)/(1+x)^4 ).
%F A366097 a(n) = (1/(n+1)) * Sum_{k=0..floor(n/3)} binomial(n+k,k) * binomial(3*n-k+3,n-3*k).
%o A366097 (PARI) a(n) = sum(k=0, n\3, binomial(n+k, k)*binomial(3*n-k+3, n-3*k))/(n+1);
%Y A366097 Cf. A366071, A366095, A366096.
%K A366097 nonn
%O A366097 0,2
%A A366097 _Seiichi Manyama_, Sep 29 2023