Published online by Cambridge University Press: 21 July 2014
Assume that $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}m$ and
$n$ are two positive integers which do not divide each other. If the set of conjugacy class sizes of primary and biprimary elements of a group
$G$ is
$\{1, m, n, mn\}$, we show that up to central factors
$G$ is a
$\{p,q\}$-group for two distinct primes
$p$ and
$q$.