Inverse sum indeg index of graphs

The inverse sum indeg index I S I (G) of a simple graph G is defined as the sum of the terms d G (u) d G (v) d G (u) + d G (v) over all edges u v of G , where d G (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. Keywords: Zagreb index, Inverse sum indeg index, Composite grap