OFFSET
9,2
COMMENTS
FORMULA
E.g.f.: ((x*c(x/2)*(1-2*x)^(-1/2))^9)/9!, where c(x) = g.f. for Catalan numbers A000108, a(0) := 0.
E.g.f.: (-1+(1-2*x)^(-1/2))^9/9!.
EXAMPLE
a(10)=135=3*binomial(10,2) increasing ternary 9-forest with n=10 vertices: there are three 9-forests (eight 1-vertex trees together with any of the three different 2-vertex trees) each with binomial(10,2)= 45 increasing labelings.
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wolfdieter Lang Sep 14 2007
STATUS
approved