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A052796
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E.g.f.: x^4*exp(x)^2.
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2
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0, 0, 0, 0, 24, 240, 1440, 6720, 26880, 96768, 322560, 1013760, 3041280, 8785920, 24600576, 67092480, 178913280, 467927040, 1203240960, 3048210432, 7620526080, 18827182080, 46022000640, 111421685760, 267412045824, 636695347200, 1504916275200
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OFFSET
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0,5
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COMMENTS
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a(n) is the number of ways that n people can form two distinct committees and then choose a president and vice president for each committee.
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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 0..1000
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 753
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FORMULA
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Recurrence: {a(1)=0, a(2)=0, a(3)=0, a(4)=24, (-2*n-2)*a(n)+(n-3)*a(n+1)}
O.g.f.:-24*x^4/(2*x-1)^5 [From Maksym Voznyy (voznyy(AT)mail.ru), Aug 12 2009]
a(n) = (n-3)*(n-2)*(n-1)*n * 2^(n-4). - Vaclav Kotesovec, Nov 27 2012
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MAPLE
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spec := [S, {B=Set(Z), S=Prod(Z, Z, Z, Z, B, B)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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MATHEMATICA
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Range[0, 30]!* CoefficientList[Series[Exp[x]^2 * x^4, {x, 0, 30}], x] (* Vincenzo Librandi, Dec 06 2012 *)
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PROG
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(MAGMA) [(n-3)*(n-2)*(n-1)*n * 2^(n-4): n in [0..30]]; // Vincenzo Librandi, Dec 06 2012
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CROSSREFS
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Equals A090802(n, 4).
Sequence in context: A192491 A167548 A192849 * A056269 A000919 A014340
Adjacent sequences: A052793 A052794 A052795 * A052797 A052798 A052799
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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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EXTENSIONS
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More terms from Vincenzo Librandi, Dec 06 2012
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STATUS
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approved
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