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 A370877 #9 Mar 04 2024 11:53:22
%S A370877 1,1,3,15,111,1095,13605,204225,3597825,72788625,1663323795,
%T A370877 42373980495,1190822561775,36596898673335,1221033470181525,
%U A370877 43954996792932225,1698138394110583425,70082689941923083425,3077205709746516423075,143235112906380591471375
%N A370877 Expansion of e.g.f. (1/x) * Series_Reversion( x/(x + exp(x^2/2)) ).
%H A370877 <a href="/index/Res#revert">Index entries for reversions of series</a>
%F A370877 a(n) = n! * Sum_{k=0..floor(n/2)} (2*k+1)^(k-1) * binomial(n,2*k)/(2^k * k!).
%o A370877 (PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(serreverse(x/(x+exp(x^2/2)))/x))
%o A370877 (PARI) a(n) = n!*sum(k=0, n\2, (2*k+1)^(k-1)*binomial(n, 2*k)/(2^k*k!));
%Y A370877 Cf. A352410, A370878.
%K A370877 nonn
%O A370877 0,3
%A A370877 _Seiichi Manyama_, Mar 03 2024