OFFSET
1,3
LINKS
J. Fulman, Mixing time for a random walk on rooted trees, The Electronic J. of Combinatorics, 16, 2009, R139.
M. E. Hoffman, Combinatorics of rooted trees and Hopf algebras, Trans. Amer. Math. Soc., 355, 2003, 3795-3811.
FORMULA
Apparently, no formula is available. The example gives a hint how the first ten terms of the sequence have been computed (using Maple).
EXAMPLE
a(4) = 12 because there are four rooted trees with 4 vertices; their Matula-Goebel numbers are 5,6,7, and 8 and, consequently M(5)+M(6)+M(7)+M(8) = 1+3+2+6 = 12 (see A206494).
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Emeric Deutsch, Jul 21 2012
EXTENSIONS
a(11)-a(16) from Alois P. Heinz, Sep 08 2012
STATUS
approved