A239753 Number of pairs of functions (f,g) on a set of n elements into itself satisfying f(x) = g(f(g(x))).

1, 1, 8, 87, 1312, 24685, 564336, 15168811

Offset

0,3

Links

Table of n, a(n) for n=0..7.

Formula

a(n) <= n^2n. - Charles R Greathouse IV, Mar 26 2014

Crossrefs

Cf. A000248, A000949.

Sequence in context: A225613 A358982 A243922 * A246512 A366233 A248471

Adjacent sequences: A239750 A239751 A239752 * A239754 A239755 A239756

Keyword

nonn,more

Author

Chad Brewbaker, Mar 26 2014

Extensions

a(6)-a(7) from Giovanni Resta, Mar 28 2014

Status

approved