OFFSET
0,3
COMMENTS
a(n) is the number of partitions of the set {1, 2, ..., 2n} into an even number of blocks, each containing an even number of elements. - Isabel C. Lugo (izzycat(AT)gmail.com), Aug 23 2004
REFERENCES
L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 226, 9th line of table.
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..250
MAPLE
seq(factorial(k)*coeftayl(cosh(cosh(x)-1), x = 0, k), k=0..200, 2); # Muniru A Asiru, Jan 29 2018
MATHEMATICA
nn = 30; Insert[Select[Range[0, nn]! CoefficientList[Series[Cosh[Cosh[x] - 1], {x, 0, nn}], x], # > 0 &], 0, 2] (* Geoffrey Critzer, Mar 31 2012 *)
With[{nn = 50}, CoefficientList[Series[Cosh[Cosh[x] - 1], {x, 0, nn}], x] Range[0, nn]!][[1 ;; ;; 2]] (* G. C. Greubel, Jan 29 2018 *)
PROG
(PARI) x='x+O('x^50); v=Vec(serlaplace(cosh(cosh(x)-1))); vector(#v\2, n, v[2*n-1]) \\ G. C. Greubel, Jan 29 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jan 28 2001
STATUS
approved