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A052686
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E.g.f. x^2*(1+3x-3x^2)/(1-x).
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0
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0, 0, 2, 24, 24, 120, 720, 5040, 40320, 362880, 3628800, 39916800, 479001600, 6227020800, 87178291200, 1307674368000, 20922789888000, 355687428096000, 6402373705728000, 121645100408832000, 2432902008176640000
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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..20.
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 634
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FORMULA
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E.g.f.: x^2*(-3*x+3*x^2-1)/(-1+x)
Recurrence: {a(1)=0, a(0)=0, (-1-n)*a(n)+a(n+1)=0, a(2)=2, a(4)=24, a(3)=24}
n!, n>3.
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MAPLE
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spec := [S, {S=Prod(Z, Z, Union(Z, Z, Z, Sequence(Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Sequence in context: A220773 A055535 A072217 * A064818 A022374 A139334
Adjacent sequences: A052683 A052684 A052685 * A052687 A052688 A052689
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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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