OFFSET
0,3
COMMENTS
The number of functions from {1,2,...,n} to itself such that f(x)=f^4(x). - Geoffrey Critzer, Sep 18 2012
REFERENCES
I. P. Goulden and D. M. Jackson, Combinatorial Enumeration, Wiley, N.Y., 1983.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..200
FORMULA
E.g.f.: exp(Sum_{d|m} T_k^d/d), where T_k = x*exp(T_(k - 1)), k >= 1, T_0 = x; k = 1, m = 3.
MATHEMATICA
nn=20; a=x Exp[x]; Range[0, nn]!CoefficientList[Series[Exp[a+a^3/3], {x, 0, nn}], x] (* Geoffrey Critzer, Sep 18 2012 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladeta Jovovic, Apr 07 2001
STATUS
approved