The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A102687 Number of different squares of mappings of a finite set of n elements into itself. 13
 1, 1, 3, 12, 100, 1075, 13356, 197764, 3403576, 66159405, 1438338070 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS 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. LINKS MATHEMATICA 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]; Table[Print[n, " ", a[n]]; a[n], {n, 0, 7}] (* Jean-François Alcover, May 27 2019 *) CROSSREFS Cf. A102709. Column k=2 of A247026. Sequence in context: A162055 A067300 A133359 * A202302 A141535 A324313 Adjacent sequences:  A102684 A102685 A102686 * A102688 A102689 A102690 KEYWORD nonn,more AUTHOR Eric Wegrzynowski (Eric.Wegrzynowski(AT)lifl.fr), Feb 03 2005 EXTENSIONS a(7) from Vladeta Jovovic, Feb 05 2005 a(8) and a(9) from Joshua Zucker, May 18 2006 a(0) from Alois P. Heinz, Sep 09 2014 a(10) from Bert Dobbelaere, Jan 24 2019 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified April 12 08:50 EDT 2021. Contains 342912 sequences. (Running on oeis4.)