A255525 1/n! times the number of ordered pairs of permutation functions f,g on n elements where f(g(g(x))) = g(f(f(x))).

1, 1, 1, 1, 2, 3, 4, 4, 6, 9, 13, 17, 27, 31, 42, 57, 83, 104

Offset

0,5

Comments

The fact that A239836(n) is a multiple of n! follows from a general result in group theory due to Solomon.

Links

Table of n, a(n) for n=0..17.

L. Solomon, The solutions of equations in groups, Arch. Math., V.20. no.3, (1969) 241-247.

Formula

a(n) = A239836(n)/n!.

Crossrefs

Cf. A239836.

Sequence in context: A290728 A296116 A017832 * A347713 A056880 A053273

Adjacent sequences: A255522 A255523 A255524 * A255526 A255527 A255528

Keyword

nonn,more,changed

Author

Paul Boddington, Feb 24 2015

Status

approved