On the Weisfeiler-Leman dimension of circulant graphs

A circulant graph is a Cayley graph of a finite cyclic group. The Weisfeiler-Leman-dimension of a circulant graph $X$ with respect to the class of all circulant graphs is the smallest positive integer~$m$ such that the $m$-dimensional Weisfeiler-Leman algorithm correctly tests the isomorphism between $X$ and any other circulant graph. It is proved that for a circulant graph of order $n$ this dimension is less than or equal to $\mathrm{\Omega }(n)+3$, where $\mathrm{\Omega }(n)$ is the number of prime divisors of~$n$.