A239785 Number of pairs of functions (f,g) from a set of n elements into itself satisfying f(g(x)) = f(g(g(x))).

1, 1, 14, 411, 19912, 1412745, 136537056, 17121680443, 2689204119680, 515064088281105, 117799925502246400, 31632261276824265651, 9834875009177533433856, 3499390123461225816417049, 1410881634834074605203513344, 639075759923134612424469976875

Offset

0,3

Links

Max Alekseyev, Table of n, a(n) for n = 0..100

Prog

(PARI) a239785(n) = if(n==1, 1, x='x+O('x^(n+1)); polcoef((1+lambertw(-x*exp(x*(n-1))))^(-n), n)) * n!; \\ Max Alekseyev, Nov 03 2025

Crossrefs

Cf. A181162, A239749, A239750, A239752, A239755, A239756, A239759, A239762, A239764, A239766, A239772, A239775, A239781, A239783.

Sequence in context: A041364 A353609 A222904 * A275025 A236156 A258392

Adjacent sequences: A239782 A239783 A239784 * A239786 A239787 A239788

Keyword

nonn

Author

Chad Brewbaker, Mar 26 2014

Extensions

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

Terms a(8) onward from Max Alekseyev, Nov 03 2025

Status

approved