Let be a finite, connected,
undirected graph with graph
diameter
and graph distance between vertices and .
A radio labeling of a graph is labeling using distinct nonnegative integers such that
for every
pair of distinct vertices ,
in the vertex
set of .
Then the radio number of ,
commonly denoted ,
is the smallest integer
such that
has a radio labeling
with .

The radio number of path graphs and cycle graphs were determined by Liu and Zhu (2005). The following table
summarizes some known results for a number of special families of graphs.

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