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A052848
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A simple grammar.
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0
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1, 0, 2, 3, 28, 125, 1146, 8827, 94200, 1007001, 12814390, 172114151, 2584755636, 41436880069, 721702509906, 13397081295795, 266105607506416, 5605474012933169, 125164378600050798, 2948082261121889983
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 816
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FORMULA
| E.g.f.: -1/(-1+x*exp(x)-x).
a(n) = n!*sum(k=0..n/2, (k!*stirling2(n-k,k))/(n-k)!). -Vladimir Kruchinin, Nov 16 2011
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MAPLE
| spec := [S, {B=Prod(Z, C), C=Set(Z, 1 <= card), S=Sequence(B)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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PROG
| (Maxima) a(n):=n!*sum((k!*stirling2(n-k, k))/(n-k)!, k, 0, n/2); [Vladimir Kruchinin, Nov 16 2011]
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CROSSREFS
| Sequence in context: A012697 A191470 A001094 * A206592 A126266 A206591
Adjacent sequences: A052845 A052846 A052847 * A052849 A052850 A052851
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KEYWORD
| nonn,easy
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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