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 A336947 #12 Aug 09 2021 03:43:32
%S A336947 1,3,14,98,920,10792,151888,2494032,46803072,988095104,23178247424,
%T A336947 598074306304,16835199087616,513385352524800,16859837094942720,
%U A336947 593234633904293888,22265289445252628480,887889931920920313856,37489832605652634763264,1670894259596134872711168
%N A336947 E.g.f.: 1 / (exp(-2*x) - x).
%F A336947 a(n) = n! * Sum_{k=0..n} (2 * (n-k+1))^k / k!.
%F A336947 a(0) = 1; a(n) = 3 * n * a(n-1) - Sum_{k=2..n} binomial(n,k) * (-2)^k * a(n-k).
%F A336947 a(n) ~ n! / ((1 + LambertW(2)) * (LambertW(2)/2)^(n+1)). - _Vaclav Kotesovec_, Aug 09 2021
%t A336947 nmax = 19; CoefficientList[Series[1/(Exp[-2 x] - x), {x, 0, nmax}], x] Range[0, nmax]!
%t A336947 Table[n! Sum[(2 (n - k + 1))^k/k!, {k, 0, n}], {n, 0, 19}]
%t A336947 a[0] = 1; a[n_] := a[n] = 3 n a[n - 1] - Sum[Binomial[n, k] (-2)^k a[n - k], {k, 2, n}]; Table[a[n], {n, 0, 19}]
%o A336947 (PARI) seq(n)={ Vec(serlaplace(1 / (exp(-2*x + O(x*x^n)) - x))) } \\ _Andrew Howroyd_, Aug 08 2020
%Y A336947 Cf. A072597, A216794, A336948, A336949, A336950.
%K A336947 nonn
%O A336947 0,2
%A A336947 _Ilya Gutkovskiy_, Aug 08 2020