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E.g.f.: 1 / (exp(-2*x) - x).
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%I #12 Aug 09 2021 03:43:32

%S 1,3,14,98,920,10792,151888,2494032,46803072,988095104,23178247424,

%T 598074306304,16835199087616,513385352524800,16859837094942720,

%U 593234633904293888,22265289445252628480,887889931920920313856,37489832605652634763264,1670894259596134872711168

%N E.g.f.: 1 / (exp(-2*x) - x).

%F a(n) = n! * Sum_{k=0..n} (2 * (n-k+1))^k / k!.

%F a(0) = 1; a(n) = 3 * n * a(n-1) - Sum_{k=2..n} binomial(n,k) * (-2)^k * a(n-k).

%F a(n) ~ n! / ((1 + LambertW(2)) * (LambertW(2)/2)^(n+1)). - _Vaclav Kotesovec_, Aug 09 2021

%t nmax = 19; CoefficientList[Series[1/(Exp[-2 x] - x), {x, 0, nmax}], x] Range[0, nmax]!

%t Table[n! Sum[(2 (n - k + 1))^k/k!, {k, 0, n}], {n, 0, 19}]

%t 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 (PARI) seq(n)={ Vec(serlaplace(1 / (exp(-2*x + O(x*x^n)) - x))) } \\ _Andrew Howroyd_, Aug 08 2020

%Y Cf. A072597, A216794, A336948, A336949, A336950.

%K nonn

%O 0,2

%A _Ilya Gutkovskiy_, Aug 08 2020