Number of leaves vs. eccentric sequence in trees

Audace A. V. Dossou-Olory1, Peter Dankelmann2
1Institut National de l’Eau and Institut de Mathematiques et de Sciences Physiques, University of Abomey-Calavi, Benin
2Department of Mathematics and Applied Mathematics, University of Johannesburg, P.O. Box 524, Auckland Park, Johannesburg 2006, South Africa

Abstract

Previous work by Lesniak (1975) and recently by Qiao and Zhan (2022) established a sharp lower bound for the number of leaves of a tree as a function of its order and diameter. In this note, we derive a lower bound for the number of leaves as a function of the entire sequence of eccentricities, and provide a complete characterisation of all trees attaining equality. We also obtain a new but simpler proof for the diameter-bound. Furthermore, we establish the analogous result for the maximum with respect to the entire eccentric sequence.

Keywords: tree, eccentric sequence, number of leaves, extremal structures, diameter