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Search: id:A068983
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| 0, 2, 23, 255, 3260, 49196, 867699, 17604595, 404662204, 10401033404, 295672787215, 9211294233871, 312080173805324, 11423999821072140, 449316582527563515, 18896039733447227131, 846135945932355895308
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OFFSET
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1,2
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COMMENT
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a(n) = number of non-injective functions [k]->[k] for 1<=k<=n.
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FORMULA
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a(n) = sigma(k^k-k!) for k = 1 to n
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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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CROSSREFS
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Cf. A036679.
Sequence in context: A110773 A088087 A088085 this_sequence A083427 A083470 A064110
Adjacent sequences: A068980 A068981 A068982 this_sequence A068984 A068985 A068986
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KEYWORD
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easy,nonn
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AUTHOR
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Darrell Minor (dminor(AT)cscc.edu), Apr 02 2002
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