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A174782
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Sum of the numerators for computing the fourth moment of the probability mass function for the number of involutions with k 2-cycles in n elements (A000085) assuming equal likelihood.
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0
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0, 1, 3, 54, 250, 1950, 10206, 64288, 350064, 2065500, 11509300, 66905256, 380767608, 2226036904, 12949377000, 76842172800, 457297336576, 2766381692688, 16849247813424, 104116268476000, 649043824951200
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OFFSET
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1,3
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COMMENTS
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Since the PMF represents a probability function, there is no unique set of numerators. That is, only the relative magnitude of the sum of the numerators matter so long as the denominator is of the same relative magnitude (since the relative magnitudes cancel upon division).
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LINKS
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FORMULA
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a(n)=Sum_{k=0..[ n/2 ]} k^4*n!/((n-2*k)!*2^k*k!).
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PROG
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(PARI) a(n) = sum(k=0, n\2 , k^4*n!/((n-2*k)!*2^k*k!)); \\ Michel Marcus, Aug 10 2013
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CROSSREFS
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First moment numerators are given by A162970. The denominator is given by A000085.
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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