Very recently, Aouchiche and Hansen gave an upper bound on the ratio of GA/chi of the geometric-arithmetic index GA(G) and the chromatic number chi(G) of a graph. Furthermore, they proposed several conjectures on the relation between geometric-arithmetic index and chromatic number, and clique number. In this note, we disprove four of those conjectures. In addition, we present a sufficient condition for an edge e is an element of E(G) with GA(G - e) < GA(G). (C) 2018 Elsevier B.V. All rights reserved.
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Univ Autonoma Guerrero, Fac Matemat, Carlos E Adame 54 Col Garita, Acapulco 39650, MexicoUniv Autonoma Guerrero, Fac Matemat, Carlos E Adame 54 Col Garita, Acapulco 39650, Mexico
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Univ Carlos III Madrid, Dept Matemat, Ave Univ 30, Madrid 28911, SpainUniv Carlos III Madrid, Dept Matemat, Ave Univ 30, Madrid 28911, Spain
Pestana, Domingo
Sigarreta, Jose M.
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Univ Autonoma Guerrero, Fac Matemat, Carlos E Adame 5, Acapulco, Gro, MexicoUniv Carlos III Madrid, Dept Matemat, Ave Univ 30, Madrid 28911, Spain
Sigarreta, Jose M.
Touris, Eva
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Univ Autonoma Madrid, Fac Ciencias, Dept Matemat, Campus Cantoblanco, E-28049 Madrid, SpainUniv Carlos III Madrid, Dept Matemat, Ave Univ 30, Madrid 28911, Spain
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S China Normal Univ, Dept Math, Guangzhou 510631, Guangdong, Peoples R ChinaS China Normal Univ, Dept Math, Guangzhou 510631, Guangdong, Peoples R China
Yuan, Yan
Zhou, Bo
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S China Normal Univ, Dept Math, Guangzhou 510631, Guangdong, Peoples R ChinaS China Normal Univ, Dept Math, Guangzhou 510631, Guangdong, Peoples R China
Zhou, Bo
Trinajstic, Nenad
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Rugjer Boskovic Inst, Zagreb 10002, CroatiaS China Normal Univ, Dept Math, Guangzhou 510631, Guangdong, Peoples R China
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Univ Carlos III Madrid, Dept Matemat, Ave Univ 30, Madrid 28911, SpainUniv Carlos III Madrid, Dept Matemat, Ave Univ 30, Madrid 28911, Spain
Rodriguez, Jose M.
Sigarreta, Jose M.
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Univ Autonoma Guerrero, Fac Matemat, Carlos E Adame 54 Col Garita, Acapulco 39650, Gro, MexicoUniv Carlos III Madrid, Dept Matemat, Ave Univ 30, Madrid 28911, Spain