eng Ansari Education and Research Society Journal of Ultra Scientist of Physical Sciences April 2010 22 1 123 126 jusps-A 1035 article Jaya Ambigavathi Ragavan (ambiga_27@yahoo.co.uk.) 1 R.Sattanathan 2 2 Research Scholar Vinayaka Mission University, Salem Associate Professor D.G. Vaishnav College, Chennai - 600106 (INDIA) <p style="text-align: justify;">An L(2,1)-labeling of a graph G is an assignment of labels from {0,1,&hellip;,n} to the vertices of G such that vertices at distance two get different labels and adjacent vertices get labels that are at least two apart. The minimum span (difference between largest and smallest labels) taken over all L(2,1)-labeling of G is the l-number of G. The aim of this paper is to determine the l-number of the join of two graphs, C_m and P_n.<br /> &nbsp;</p> https://www.ultrascientist.org/paper/1035/ L(2,1)-labeling l-number join of two graphs.