A proper coloring of a graph $G$ is a function from the vertices of the graph to a set of colors such that any two adjacent vertices have different colors, and the chromatic number of $G$ is the minimum number of colors needed in a proper coloring of a graph. In this paper, we will find the chromatic number of the Harary graphs, which are the circulant graphs in some cases.
Adel P. Kazemi. Parvin Jalilolghadr. "Chromatic number of Harary graphs." Tbilisi Math. J. 9 (1) 271 - 278, June 2016. https://doi.org/10.1515/tmj-2016-0013