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A226223
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The number of endomorphisms of the full transformation monoid on the set {1..n}.
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2
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1, 7, 40, 345, 3226, 38503, 529614, 8219025, 141633028, 2677676931, 55021969234, 1219667932585, 28986449652564, 734758590703803, 19777243624646566, 563105619051710817, 16902630001714260832, 533291777845757001523, 17638752528002502032130, 610137644831701323189321
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OFFSET
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1,2
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LINKS
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PROG
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(PARI) a(n)=if(n<5, return([1, 7, 40, 345][n])); n!*(sum(m=1, n, m^(n-m)*sum(k=0, (m-1)\2, sum(r=1, m-2*k, r^(m-k-r)/(m-2*k-r)!/r!)/2^k/k!)/(n-m)!)+1) \\ Charles R Greathouse IV, May 31 2013
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CROSSREFS
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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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