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 A363817 #10 Oct 18 2023 09:58:37
%S A363817 1,4,5,15,-5,111,-402,2172,-10892,57362,-305756,1656560,-9083341,
%T A363817 50328219,-281324174,1584578882,-8984740332,51242962422,-293772467974,
%U A363817 1691974930794,-9785378133066,56805049768410,-330880419984556,1933299689139664,-11328101469158229
%N A363817 G.f. satisfies A(x) = (1 + x/A(x))/(1 - x)^3.
%F A363817 G.f.: A(x) = -2*x / (1-sqrt(1+4*x*(1-x)^3)).
%F A363817 a(n) = (-1)^(n-1) * Sum_{k=0..n} binomial(2*k-1,k) * binomial(3*(k-1),n-k)/(2*k-1).
%o A363817 (PARI) a(n) = (-1)^(n-1)*sum(k=0, n, binomial(2*k-1, k)*binomial(3*(k-1), n-k)/(2*k-1));
%Y A363817 Cf. A366363, A363816.
%K A363817 sign
%O A363817 0,2
%A A363817 _Seiichi Manyama_, Oct 18 2023