Multi-distance granularity structural α-subtree index of generalized Bethe trees

In graph theory and its applications, trees, BC-trees, subtrees and BC-subtrees have been extensively studied. We introduce a generalization of the BC-tree, called the multi-granular α-tree, which is a tree (of order at least α+1) where any two leaves are at a distance that is a multiple of α. We study the number of α-subtrees, through α-subtree generating functions, for generalized Bethe trees, Bethe trees and dendrimers (hyper-branched structures in molecular topology). Our results can also be used to examine the asymptotic behavior of the average order of α-subtrees in dendrimers.