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A052857 A simple grammar. 0
0, 1, 2, 15, 184, 3145, 68976, 1846999, 58413440, 2130740721, 88061420800, 4066862460991, 207556068584448, 11600364266112505, 704664527894104064, 46226086991634882375, 3256882066245640093696, 245279323467051422886241 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..17.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 825

FORMULA

E.g.f.: exp(RootOf(exp(_Z)*x*_Z+exp(_Z)*x-_Z))*x

a(n)=((n-1)!*sum(k=1..n-1, (n^k*binomial(n-2,k-1))/k!)), a(1)=1. [From Vladimir Kruchinin, May 10 2011]

MAPLE

spec := [S, {C=Set(B), S=Prod(Z, C), B=Sequence(S, 1<= card)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);

PROG

(Maxima)

a(n):=if n=1 then 1 else ((n-1)!*sum((n^k*binomial(n-2, k-1))/k!, k, 1, n-1)); [From Vladimir Kruchinin, May 10 2011]

CROSSREFS

Sequence in context: A208409 A196792 A210655 * A053492 A208402 A098343

Adjacent sequences:  A052854 A052855 A052856 * A052858 A052859 A052860

KEYWORD

easy,nonn

AUTHOR

encyclopedia(AT)pommard.inria.fr, Jan 25 2000

STATUS

approved

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Last modified October 25 22:57 EDT 2014. Contains 248564 sequences.