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 A370839 #11 Mar 03 2024 09:52:56
%S A370839 1,1,1,0,-5,-21,-59,-117,-96,473,3065,10946,27425,39787,-46771,
%T A370839 -598587,-2607973,-7726692,-15044242,-3990122,123643981,680120511,
%U A370839 2337866969,5550672915,6054525814,-23115014733,-181704066985,-726923651722,-2017980693299,-3365063873213
%N A370839 Expansion of (1/x) * Series_Reversion( x * (1/(1-x^2) - x) ).
%H A370839 <a href="/index/Res#revert">Index entries for reversions of series</a>
%F A370839 a(n) = (1/(n+1)) * Sum_{k=0..floor(n/2)} (-1)^k * binomial(2*n-2*k+1,k) * binomial(2*n-2*k,n-2*k).
%o A370839 (PARI) my(N=40, x='x+O('x^N)); Vec(serreverse(x*(1/(1-x^2)-x))/x)
%o A370839 (PARI) a(n) = sum(k=0, n\2, (-1)^k*binomial(2*n-2*k+1, k)*binomial(2*n-2*k, n-2*k))/(n+1);
%Y A370839 Cf. A370840, A370841.
%Y A370839 Cf. A199874.
%K A370839 sign
%O A370839 0,5
%A A370839 _Seiichi Manyama_, Mar 03 2024