Multiplicative Zagreb indices of k-trees

Let G be a graph with vertex set V(G) and edge set E(G). The first generalized multiplicative Zagreb index of G is Pi(1,c)(G) = Pi(v is an element of V(G)) d(v)(c), for a real number c > 0, and the second multiplicative Zagreb index is Pi(2)(G) = Pi(uv is an element of E(G)) d(u)d(v), where d(u), d(v) are the degrees of the vertices of u, v. The multiplicative Zagreb indices have been the focus of considerable research in computational chemistry dating back to Narumi and Katayama in 1980s. In this paper, we generalize Narumi Katayama index and the first multiplicative index, where c = 1, 2, respectively, and extend the results of Gutman to the generalized tree, the k-tree, where the results of Gutman are for k = 1. Additionally, we characterize the extremal graphs and determine the exact bounds of these indices of k-trees, which attain the lower and upper bounds. (C) 2014 Elsevier B.V. All rights reserved.