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A126232
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Number of functions f:{1,2,...,n}->{1,2,...,n} such that Im(f) contains 5 fixed elements.
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1
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120, 2520, 52080, 1164240, 28594440, 771309000, 22746757440, 729419296320, 25295774463960, 943934414262840, 37728367833920400, 1608541146018621360, 72881990543360522280, 3497670707401587171240, 177254235519701336515680
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OFFSET
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5,1
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LINKS
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FORMULA
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a(n)=n^n-5*(n-1)^n+10*(n-2)^n-10*(n-3)^n+5*(n-4)^n-(n-5)^n.
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EXAMPLE
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a(10)=771309000.
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MAPLE
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a(n):n->n^n-5*(n-1)^n+10*(n-2)^n-10*(n-3)^n+5*(n-4)^n-(n-5)^n;
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MATHEMATICA
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Drop[Table[Sum[(-1)^k Binomial[5, k] (n-k)^n, {k, 0, 5}], {n, 1, 20}], 4] (* Geoffrey Critzer, Dec 23 2012 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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