OFFSET
0,2
COMMENTS
Sequence appears in the problem of normal ordering of functions of boson operators.
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..447
FORMULA
a(n) = ((-1)^n*n!/e)*Sum_{k>=0} L(n,-n-2,k)/k!, where L is a generalized Laguerre polynomial.
a(n) = Sum_{k=0..n} binomial(n,k)*(k + 1)!*Bell(n-k), where Bell() = A000110. - Ilya Gutkovskiy, May 24 2018
a(n) ~ exp(exp(1)-1) * n * n!. - Vaclav Kotesovec, Jun 26 2022
MAPLE
egf := exp(exp(x)-1)/((1-x)^2);
seq(n!*coeff(series(egf, x, n+1), x, n), n=0..21); # Peter Luschny, Sep 17 2014
MATHEMATICA
With[{nmax = 50}, CoefficientList[Series[Exp[Exp[x] - 1]/(1 - x)^2, {x, 0, nmax}], x]*Range[0, nmax]!] (* G. C. Greubel, May 23 2018 *)
PROG
(PARI) x='x+O('x^30); Vec(serlaplace(exp(exp(x)-1)/(1-x)^2 )) \\ G. C. Greubel, May 23 2018
(Magma) m:=25; R<x>:=PowerSeriesRing(Rationals(), m); b:=Coefficients(R!(Exp(Exp(x)-1)/(1-x)^2)); [Factorial(n-1)*b[n]: n in [1..m]]; // G. C. Greubel, May 23 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Karol A. Penson, Nov 29 2004
STATUS
approved