Extremal values of vertex-degree-based topological indices over hexagonal systems with fixed number of vertices.

Let G be a graph with n vertices. A vertex-degree-based topological index is defined from a set of real numbers {ψij} as TI (G) = Σ1⩽i⩽j⩽n-1mijψij where mij is the number of edges of G connecting a vertex of degree i with a vertex of degree j . Many of the well-known topological indices are particular cases of this expression, including all Randic-type connectivity indices. In this work we determine extremal values for TI over the set HSn of hexagonal systems with a fixed number of vertices. [ABSTRACT FROM AUTHOR]