Abstract
The acyclic chromatic number a(G) of a graph G is the minimum number of colors such that G has a proper vertex coloring and no bichromatic cycles. For a graph G with maximum degree $$\Delta $$ , Grunbaum (1973) conjectured $$a(G)\le \Delta +1$$ . Up to now, the conjecture has only been shown for $$\Delta \le 4$$ . In this paper, it is proved that $$a(G)\le 12$$ for $$\Delta =7$$ , thus improving the result $$a(G)\le 17$$ of Dieng et al. (in: Proc. European conference on combinatorics, graph theory and applications, 2010).
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