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Sharp bounds of the Zagreb indices of $$k$$-trees. (English) Zbl 1318.90070
Summary: For a graph $$G$$, the first Zagreb index $$M _{1}$$ is equal to the sum of squares of the vertex degrees, and the second Zagreb index $$M _{2}$$ is equal to the sum of the products of degrees of pairs of adjacent vertices. The Zagreb indices have been the focus of considerable research in computational chemistry dating back to I. Gutman and N. Trinajstić [“Graph theory and molecular orbitals. Total $$\pi$$-electron energy of alternate hydrocarbons”, Chem. Phys. Lett. 17. 535–538 (1972)]. In 2004, I. Gutman and K. Ch. Das [MATCH Commun. Math. Comput. Chem. 50, 83–92 (2004; Zbl 1053.05115)] determined sharp upper and lower bounds for $$M _{1}$$ and $$M _{2}$$ values for trees along with the unique trees that obtain the minimum and maximum $$M _{1}$$ and $$M _{2}$$ values respectively. In this paper, we generalize the results of Gutman and Das [loc. cit.] to the generalized tree, the $$k$$-tree, where the results of Gutman and Das [loc. cit.] are for $$k=1$$. Also by showing that maximal outerplanar graphs are 2-trees, we also extend a result of A. Hou et al. [J. Comb. Optim. 22, No. 2, 252–269 (2011; Zbl 1250.90102)] who determined sharp upper and lower bounds for $$M _{1}$$ and $$M _{2}$$ values for maximal outerplanar graphs.

##### MSC:
 90C35 Programming involving graphs or networks 90C27 Combinatorial optimization
##### Citations:
Zbl 1053.05115; Zbl 1250.90102
Full Text:
##### References:
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