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Estimating the Estrada index |
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| Authors: | José Antonio de la Peña Ivan Gutman |
| Institution: | a Instituto de Matemáticas, UNAM, Circuito Exterior, Ciudad Universitaria, Mexico 04510, DF, Mexico b Faculty of Science, University of Kragujevac, P.O. Box 60, 34000 Kragujevac, Serbia c Departamento de Matemática, Universidad de Los Andes Mérida 5101, Venezuela |
| Abstract: | Let G be a graph on n vertices, and let λ1,λ2,…,λn be its eigenvalues. The Estrada index of G is a recently introduced graph invariant, defined as  . We establish lower and upper bounds for EE in terms of the number of vertices and number of edges. Also some inequalities between EE and the energy of G are obtained. |
| Keywords: | 05C50 05C90 |
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