Second and Third Extremals of Catacondensed Hexagonal Systems with Respect to the PI Index

Document Type : Research Paper


1 Islamic Azad University, Khorramabad Branch, I. R. Iran

2 Arak University, Iran


The Padmakar-Ivan (PI) index is a Wiener-Szeged-like topological index which reflects certain structural features of organic molecules. The PI index of a graph G is the sum of all edges uv of G of the number of edges which are not equidistant from the vertices u and v. In this paper we obtain the second and third extremals of catacondensed hexagonal systems with respect to the PI index.