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Topological index is a numerical descriptor of a molecule, based on a certain topological feature of the corresponding molecular graph, it is found that there is a strong correlation between the properties of chemical compounds and their molecular structure. In the other side, titania nanotube is a well-known semiconductor and has numerous technological applications such as biomedical devices, dye-sensitized solar cells, and etc. In this paper, the second Hyper-Zagreb index and their coindex of Titania nanotubes have been computed. Furthermore, strong correlation coefficients between second Hyper-Zagreb index and some physicochemical properties such as Density (DENS), Molar volume (MV), Acentric factor (Acenfac) and Entropy (S) have been Appeared.

A topological index of graph \(G\) is a numerical parameter related to graph which characterizes its molecular topology and is usually graph invariant. Topological indices are widely used to determine the correlation between the specific properties of molecules and the biological activity with their configuration in the study of quantitative structure-activity relationships (QSARs). In this paper some basic mathematical operations for the forgotten index of complement graph operations such as join \(\overline {G_1+G_2}\), tensor product \(\overline {G_1 \otimes G_2}\), Cartesian product \(\overline {G_1\times G_2}\), composition \(\overline {G_1\circ G_2}\), strong product \(\overline {G_1\ast G_2}\), disjunction \(\overline {G_1\vee G_2}\) and symmetric difference \(\overline {G_1\oplus G_2}\) will be explained. The results are applied to molecular graph of nanotorus and titania nanotubes.