A topological index is a real number related to the structure of a connected graph G and is invariant under graph automorphism. Let G be a (molecular) graph possessing n vertices and m edges, and e=x,y be an edge of G and x, y are two of its vertices, then the distance d(x,y)=d(x,y|G) between the vertices x and y is equal to the length of the shortest path that connects them in G. The goal of t...

The Merrifield-Simmons index of a graph is defined as the total number of the independent sets of the graph and the Hosoya index of a graph is defined as the total number of the matchings of the graph. In this paper, we give formula for Merrifield-Simmons and Hosoya indices of some classes of cartesian product of two graphs K{_2}×H, where H is a path graph P{_n}, cyclic graph C{_n}, or star gra...

We characterize the trees T with n vertices whose Hosoya index (total number of matchings) is Z(T ) > 16fn−5 resp. the trees whose Merrifield-Simmons index (total number of independent subsets) is σ(T ) < 18fn−5 + 21fn−6, where fk is the kth Fibonacci number. It turns out that all the trees satisfying the inequality are tripodes (trees with exactly three leaves) and the path in both cases. Furt...

Let R be a commutative ring with nonzero identity and let id="M2"> Z its set of zero divisors. The zero-divisor graph id="M3"> is the id="M4"> ? vertex id="M5"> V = ? , wh...

Let T be an acyclic graph without perfect matching and Z(T ) be its Hosoya index; let Fn be the nth Fibonacci number. It is proved in this work that Z(T ) ≤ 2F2m F2m+1 when T has order 4m with the equality holding if and only if T = T1,2m−1,2m−1, and that Z(T ) ≤ F2 2m+2 + F2m F2m+1 when T has order 4m + 2 with the equality holding if and only if T = T1,2m+1,2m−1, where m is a positive integer ...

It was recently shown that an interesting class of trees maximizes the MerrifieldSimmons index and minimizes the Hosoya index and energy among all trees with given number of vertices and maximum degree. In this paper, we describe how these trees (which we will call F-trees) can be constructed algorithmically by means of so-called F-expansions, which are very similar to ordinary base-d digital e...

Abstract Many chemical indices have been invented in theoretical chemistry, such as Wiener index, Merrifield-Simmons index, Hosoya index, spectral radius and Randić index, etc. The extremal trees and unicyclic graphs for these chemical indices are interested in existing literature. Let G be a molecular graph (called a cacti), which all of blocks of G are either edges or cycles. Denote G (n, r) ...