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 A336310 #14 Jul 18 2020 03:07:16
%S A336310 0,0,2,24,300,4260,69120,1271340,26233200,601246800,15171105600,
%T A336310 418203324000,12509695598400,403696590897600,13982667790291200,
%U A336310 517482647165484000,20381726051118432000,851302665544050720000,37587618060140244096000,1749369290830388555328000,85599487854917373617280000
%N A336310 Sum of path lengths over all labeled rooted unordered binary trees.
%F A336310 E.g.f.: ((1 -sqrt(1 -2*z -z^2))*(1 -z -sqrt(1 -2*z -z^2)))/(z*(1 -2*z -z^2)).
%F A336310 a(n) = Sum_{k} A336309(n,k)*k, for n>=1.
%F A336310 a(n) ~ n!/2 * (sqrt(2) + 1)^(n+1) * (1 - sqrt((10-sqrt(2))/(Pi*n))). - _Vaclav Kotesovec_, Jul 17 2020
%t A336310 nn = 20; Range[0, nn]! CoefficientList[ Series[-(((-1 + Sqrt[1 - 2 z - z^2]) (-1 + z + Sqrt[1 - 2 z - z^2]))/(z (-1 + 2 z + z^2))), {z, 0, nn}], z]
%o A336310 (PARI) my(z='z+O('z^25)); concat([0,0], Vec(serlaplace(((1 -sqrt(1 -2*z -z^2))*(1 -z -sqrt(1 -2*z -z^2)))/(z*(1 -2*z -z^2))))) \\ _Joerg Arndt_, Jul 18 2020
%Y A336310 Cf. A336309, A036774 (row sums).
%K A336310 nonn
%O A336310 0,3
%A A336310 _Geoffrey Critzer_, Jul 17 2020