On planarity and colorability of circulant graphs

For given positive integers n,a"1,...,a"m, we consider the undirected circulant graph G=(V,E) with set of vertices V={0,...,n-1} and set of edges E={[i,j]:i-j=+/-a"k(modn) for some 1==3. For m=2 we completely characterize planarity. It is shown that G is bipartite if and only if there is an l such that 2^l divides a"1,...,a"m,2^l^+^1|n, but 2^l^+^1@?a"j for 1=