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 A377890 #11 Dec 29 2024 08:48:54
%S A377890 1,2,15,211,4433,124741,4412815,188335981,9421966209,540884623753,
%T A377890 35054089163351,2531882857204273,201689970517618225,
%U A377890 17567711167993834381,1661084543502646535967,169448367505003640681221,18550123929621138841581185,2169272360350263071212545553
%N A377890 E.g.f. A(x) satisfies A(x) = (1 + x*A(x)^2) * exp(x * A(x)).
%F A377890 a(n) = n! * Sum_{k=0..n} (2*n-k+1)^(k-1) * binomial(2*n-k+1,n-k)/k!.
%F A377890 E.g.f.: (1/x) * Series_Reversion( x * (exp(-x) - x) ). - _Seiichi Manyama_, Dec 29 2024
%o A377890 (PARI) a(n) = n!*sum(k=0, n, (2*n-k+1)^(k-1)*binomial(2*n-k+1, n-k)/k!);
%Y A377890 Cf. A088690, A377826, A377891.
%K A377890 nonn
%O A377890 0,2
%A A377890 _Seiichi Manyama_, Nov 11 2024