OFFSET
0,3
COMMENTS
Related to generalized Catalan numbers; in particular, C(3n,n)/(2n+1) (enumerates ternary trees and also non-crossing trees)(A001764) and sum of root degrees of all noncrossing trees on nodes on a circle (A006629).
These numbers are cardinalities of some intervals in the Tamari lattices. - F. Chapoton, Jul 15 2021
EXAMPLE
{1}, {1,2}, {3,4,7}, {12,15,18,30}, {55,67,76,88,143}, {273,328,364,400,455,728},...
CROSSREFS
KEYWORD
AUTHOR
Paul D. Hanna, Jul 18 2002
STATUS
approved