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A068983
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a(n) = Sum_{k=0..n} (k^k-k!).
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0
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0, 2, 23, 255, 3260, 49196, 867699, 17604595, 404662204, 10401033404, 295672787215, 9211294233871, 312080173805324, 11423999821072140, 449316582527563515, 18896039733447227131, 846135945932355895308, 40192537618855187742732, 2018612071634068368034711
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OFFSET
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1,2
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COMMENTS
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a(n) = number of non-injective functions [k]->[k] for 1<=k<=n.
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LINKS
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FORMULA
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a(n) = Sum_{k=0..n} (k^k-k!).
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EXAMPLE
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a(4) = 255 because (1^1-1!)+(2^2-2!)+(3^3-3!)+(4^4-4!) = 255.
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MATHEMATICA
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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