  In this paper we study prime graphs of finite groups. The prime graph of a
finite group $G$, also known as the Gruenberg-Kegel graph, is the graph with
vertex set {primes dividing $|G|$} and an edge $p$-$q$ if and only if there
exists an element of order $pq$ in $G$. In finite group theory, studying the
prime graph of a group has been an important topic for the past almost half
century. Only recently prime graphs of solvable groups have been characterized
in graph theoretical terms only. In this paper, we continue this line of
research and give complete characterizations of several classes of groups,
including groups of square-free order, metanilpotent groups, groups of
cube-free order, and, for any $n\in \mathbb{N}$, solvable groups of
$n^\text{th}$-power-free order. We also explore the prime graphs of groups
whose composition factors are cyclic or $A_5$ and draw connections to a
conjecture of Maslova. We then propose an algorithm that recovers the prime
graph from a dual prime graph.
