OFFSET
1,3
COMMENTS
An even tree is an ordered tree in which each vertex has an even outdegree. In the preorder traversal of an ordered tree, any transition from a node at a deeper level to a node on a strictly higher level is called a jump; the positive difference of the levels is called the jump distance; the sum of the jump distances in a given ordered tree is called the jump-length.
The Krandick reference considers jumps and jump-length only in full binary trees.
LINKS
W. Krandick, Trees and jumps and real roots, J. Computational and Applied Math., 162, 2004, 51-55.
FORMULA
a(n) = (n-1)(2n-1)C(3n,n)/[3(n+1)/(2n+1)].
a(n) = Sum_{k=0..n-1} k*A127535(n,k).
D-finite with recurrence 2*(n-2)*(2*n+1)*(2*n-3)*(n+1)*a(n) -3*(n-1)*(3*n-1)*(2*n-1)*(3*n-2)*a(n-1)=0. - R. J. Mathar, Jul 26 2022
MAPLE
seq((n-1)*(2*n-1)*binomial(3*n, n)/3/(n+1)/(2*n+1), n=1..25);
CROSSREFS
KEYWORD
nonn
AUTHOR
Emeric Deutsch, Jan 19 2007
STATUS
approved