In general, a topological index, sometimes also known as a graph-theoretic index, is a numerical invariant of a chemical graph (Plavšić et al. 1993). Particular topological indices include the Balaban index, Harary index, molecular topological index, and Wiener index. Unless otherwise stated, hydrogen atoms are usually ignored in the computation of such indices as organic chemists usually do when they write a benzene ring as a hexagon. "The" topological index of a graph index defined by TI = left bracketing bar A + D right bracketing bar , where A is the adjacency matrix, D is the graph distance matrix, and left bracketing bar A + D right bracketing bar denotes the determinant of the matrix addition.