Abstract
Let d(u;v) denote the distance between two distinct vertices of a connected graph G; and diam(G) be the diameter of G. A radio labeling c of G is an assignment of positive integers to the vertices of G satisfying d(u;v)+vertical bar c(u)-c(v)vertical bar >= diam (G)+1 for every two distinct vertices u,v. The maximum integer in the range of the labeling is its span. The radio number of G, rn(G), is the minimum possible span of any radio labeling for G. In this paper, the radio numbers of Mongolian tent graph, diamond graph, fan and double fan are determined