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.
Table of n, a(n) for n=1..9.
Sequence in context: A162055 A067300 A133359 * A202302 A141535 A111485
Adjacent sequences: A102684 A102685 A102686 * A102688 A102689 A102690
Eric Wegrzynowski (Eric.Wegrzynowski(AT)lifl.fr), Feb 03 2005
a(7) from Vladeta Jovovic, Feb 05 2005
a(8) and a(9) from Joshua Zucker, May 18 2006