Let G be a finite group and π(G) = {p1,p2,…,Pk} be the set of the primes dividing the order of G. We define its prime graph Γ(G) as follows. The vertex set of this graph is π(G), and two distinct vertices p, q are joined by an edge if and only if pq ∈ πe(G). In this case, we write p～q. For p∈π(G), put deg(p):= |{q ∈π(G)|p～q}|,which is called the degree of p. We also define D(G):=(deg(p1), deg(p2),…, deg(pk)), where P1