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A052857
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A simple grammar.
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0
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0, 1, 2, 15, 184, 3145, 68976, 1846999, 58413440, 2130740721, 88061420800, 4066862460991, 207556068584448, 11600364266112505, 704664527894104064, 46226086991634882375, 3256882066245640093696, 245279323467051422886241
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listen;
history;
text;
internal format)
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OFFSET
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0,3
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LINKS
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Table of n, a(n) for n=0..17.
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 825
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FORMULA
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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]
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MAPLE
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spec := [S, {C=Set(B), S=Prod(Z, C), B=Sequence(S, 1<= card)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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PROG
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(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]
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CROSSREFS
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Sequence in context: A208409 A196792 A210655 * A053492 A208402 A098343
Adjacent sequences: A052854 A052855 A052856 * A052858 A052859 A052860
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KEYWORD
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easy,nonn
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AUTHOR
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encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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STATUS
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approved
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