MODULAR COLORINGS OF CIRCULAR HALIN GRAPHS OF LEVEL TWO

For k2, a modular k-coloring of a graph G without isolated vertices is a coloring of the vertices of G with the elements in zk having the property that for every two adjacent vertices of G, the sums of the colors of their neighbours are different in zk.The minimum k for which G has a modular k-coloring is the modular chromatic number of G. In this paper, we determine the modular chromatic number of circular Halin graph.