Inverse sum indeg index of graphs

The inverse sum indeg index ISI(G) of a simple graph G is defined as the sum of the terms dG(u)dG(v)dG(u)+dG(v) over all edges uv of G, where dG(u) denotes the degree of a vertex u of G. In this paper, we present several upper and lower bounds on the inverse sum indeg index in terms of some molecular structural parameters and relate this index to various well-known molecular descriptors.