OFFSET
1,3
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..200
C. Banderier, J.-M. Le Bars and V. Ravelomanana, Generating functions for kernels of digraphs
FORMULA
a(n) = (n-1)!*[x^n](LambertW(-LambertW(-2x)/2)). - Jean-François Alcover, Dec 13 2018
a(n) ~ 2^n * n^(n-2) / (1 + 1/LambertW(1/2)). - Vaclav Kotesovec, Feb 24 2019
MATHEMATICA
terms = 17;
Rest[CoefficientList[LambertW[-LambertW[-2x]/2] + O[x]^(terms+1), x]]* Range[0, terms-1]! (* Jean-François Alcover, Dec 13 2018 *)
PROG
(PARI) seq(n)={Vec(serlaplace(lambertw(-lambertw(-2*x + O(x*x^n))/2)/x))} \\ Andrew Howroyd, Dec 13 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Ralf Stephan, Aug 17 2004
STATUS
approved