The eccentric connectivity index of nanotubes and nanotori

Let G be a molecular graph. The eccentric connectivity index ξ c ( G ) is defined as ξ c ( G ) = ∑ u ∈ V ( G ) d e g G ( u ) ε G ( u ) , where d e g G ( u ) denotes the degree of vertex u and ε G ( u ) is the largest distance between u and any other vertex v of G . In this paper exact formulas for the eccentric connectivity index of T U C 4 C 8 ( S ) nanotube and T C 4 C 8 ( S ) nanotorus are given.