The sum number of the subdivision graph J_n~* of the umbrella
Hui Yong Yu · Journal of Jilin Institute of Chemical Technology · 2006
Umbrella J~_n is a graph of adding a hanging line in the axis K_1 of wheel W_n=C_n∨K_1.The sum number σ(G) of G is the smallest number of isolated vertices which when added to G result in a sum graph.The paper proves that σ(J~_n)2 when n2.