The Wiener index is one of the main descriptors that correlate a chemical compound’s molecular graph with experimentally gathered data regarding the compound’s characteristics. A long standing conjecture on the Wiener index ([4], [5]) states that for any positive integer n (except numbers from a given 49 element set), one can find a tree with Wiener index n. In this paper, we prove that every i...

The distance d(u, v|G) between the vertices u and v of a molecular graph G is the length of a shortest u, v-path. We consider a class of Wiener–type topological indices Wλ(G) , defined as the sum of the terms d(u, v|G) λ over all pairs of vertices of G . Several special cases of Wλ(G) , namely for λ = +1 (the original Wiener number) as well as for λ = −2,−1,+1/2,+2 and +3 , were previously stud...

Let G be a connected graph and ξ(G) = Sze(G)−We(G), where We(G) denotes the edge Wiener index and Sze(G) denotes the edge Szeged index of G. In an earlier paper, it is proved that if T is a tree then Sze(T ) = We(T ). In this paper, we continue our work to prove that for every connected graph G, Sze(G) ≥ We(G) with equality if and only if G is a tree. We also classify all graphs with ξ(G) ≤ 5. ...

The diffraction by impenetrable wedges having arbitrary aperture angle is studied by means of the Wiener-Hopf (W-H) technique. A system of functional equations called generalized Wiener-Hopf equations (GWHE) is obtained. Only for certain values of the aperture angle these equations are recognizable as standard or classical Wiener-Hopf equations (CWHE). However, in all cases, a mapping to a suit...

Given a tree T = (V,E), the second Zagreb index of T is denoted by M2(T ) = ∑ uv∈E d(u)d(v) and the Wiener polarity index of T is equal to WP (T ) = ∑ uv∈E(d(u)−1)(d(v)−1). Let π = (d1, d2, ..., dn) and π′ = (d1, d2, ..., dn) be two different non-increasing tree degree sequences. We write π π′, if and only if ∑n i=1 di = ∑n i=1 d ′ i, and ∑j i=1 di ≤ ∑j i=1 d ′ i for all j = 1, 2, ..., n. Let Γ...

The hyper-Kirchhoff index is introduced when the hyper-Wiener operator is applied to the resistance-distance matrix of a connected graph. We give lower and upper bounds for the hyper-Kirchhoff index, and determine the n-vertex unicyclic graphs with the smallest, the second and the third smallest as well as the largest, the second and the third largest hyper-Kirchhoff indices for n ≥ 5. We also ...