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A102687
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Number of different squares of labeled mappings of a finite set of n elements into itself.
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15
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1, 1, 3, 12, 100, 1075, 13356, 197764, 3403576, 66159405, 1438338070
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OFFSET
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0,3
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COMMENTS
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Let A be a finite set of cardinal n, F be the set of mappings from A to A and F_2 be the subset of F including all g such that there exists f in F with g = fof (composition of f with itself). Then a(n) = #F_2.
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LINKS
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MATHEMATICA
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f[a_][b_] /; Length[a]==Length[b] := Table[b[[a[[i]]]], {i, 1, Length[a]}];
A[n_, k_] := Nest[f[#], Range[n], k]& /@ Tuples[Range[n], {n}] // Union // Length;
a[n_] := a[n] = A[n, 2];
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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Eric Wegrzynowski (Eric.Wegrzynowski(AT)lifl.fr), Feb 03 2005
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EXTENSIONS
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STATUS
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approved
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