Tricyclic graph with maximal Estrada index

Let G be a simple connected graph on n vertices and λ 1 , λ 2 , ? , λ n be the eigenvalues of the adjacency matrix of G . The Estrada index of G is defined as E E ( G ) = ? i = 1 n e λ i . Let T n be the class of tricyclic graphs G on n vertices. In this paper, the graphs in T n with the maximal Estrada index is characterized.

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