the prime graph $gamma(g)$ of a group $g$ is
a graph with vertex set $pi(g)$, the set of primes dividing the
order of $g$, and two distinct vertices $p$ and $q$ are adjacent
by an edge written $psim q$ if there is an element in $g$ of
order $pq$. let $pi(g)={p_{1},p_{2},...,p_{k}}$. for
$pinpi(g)$, set $deg(p):=|{q inpi(g)| psim q}|$, which is
called the degree of $p$. we also set
$d(g):...