Variations on the Thompson theorem

Abstract

Thompson's theorem stated that a finite group $G$ is solvable if and only if every $2$-generated subgroup of $G$ is solvable. In this paper, we prove some new criteria for both solvability and nilpotency of a finite group using certain condition on $2$-generated subgroups. We show that a finite group $G$ is solvable if and only if for every pair of two elements $x$ and $y$ in $G$ of coprime prime power order, if $\langle x,y\rangle$ is solvable, then $\langle x,y^g\rangle$ is solvable for all $g\in G$. Similarly, a finite group $G$ is nilpotent if and only if for every pair of elements $x$ and $y$ in $G$ of coprime prime power order, if $\langle x,y\rangle$ is solvable, then $x$ and $y^g$ commute for some $g\in G.$ Some applications to graphs defined on groups are given.