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 A366403 #12 Oct 09 2023 11:19:44
%S A366403 1,2,1,2,0,4,-5,16,-35,92,-231,604,-1584,4214,-11297,30538,-83096,
%T A366403 227476,-625991,1730788,-4805594,13393690,-37458329,105089230,
%U A366403 -295673993,834086422,-2358641375,6684761126,-18985057350,54022715452,-154000562757,439742222072
%N A366403 G.f. A(x) satisfies A(x) = (1 + x / sqrt(A(x))) / (1 - x).
%F A366403 a(n) = (-1)^(n-1) * Sum_{k=0..n} binomial(3*k/2-1,k) * binomial(k/2-1,n-k) / (3*k/2-1).
%o A366403 (PARI) a(n) = (-1)^(n-1)*sum(k=0, n, binomial(3*k/2-1, k)*binomial(k/2-1, n-k)/(3*k/2-1));
%Y A366403 Cf. A366363, A366400, A366401, A366402, A366404, A366405, A366406, A366407.
%K A366403 sign
%O A366403 0,2
%A A366403 _Seiichi Manyama_, Oct 09 2023