Some new upper bounds for the inverse sum indeg index of graphs

Akbar Ali (College of Science, University of Hail, Hail)
Marjan Matejic
Emina Milovanovic
Igor Milovanovic

Electronic Journal of Graph Theory and Applications (EJGTA)
Vol 8, No 1 (2020): Electronic Journal of Graph Theory and Applications

Let G = (V,E) be a simple connected graph with the vertex set V = {1,2,...,n} and sequence of vertex degrees (d1,d2,...,dn) where di denotes the degree of a vertex i ∈ V. With i ∼ j, we denote the adjacency of the vertices i and j in the graph G. The inverse sum indeg (ISI) index of the graph G is defined as ISI(G)=∑i∼j(didj)/(di+dj). Some new upper bounds for the ISI index are obtained in this paper.