ON ESTRADA INDEX

Let G be a graph with n vertices and let ‚1;‚2;:::;‚n be its eigenvalues. The Estrada index of G is EE(G) = n P i=1 e ‚i . We present some lower and upper bounds for EE(G) in terms of graph invariants such as the number of vertices, the number of edges, the spectral moments, the flrst Zagreb index, the nullity and the largest eigenvalue.

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