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Rank and order of a finite group admitting a Frobenius group of automorphisms
E. I. Khukhro Sobolev Institute of Mathematics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
Abstract:
Suppose that a finite group
$G$ admits a Frobenius group
$FH$ of automorphisms of coprime order with kernel
$F$ and complement
$H$. For the case where
$G$ is a finite
$p$-group such that
$G=[G,F]$, it is proved that the order of
$G$ is bounded above in terms of the order of
$H$ and the order of the fixed-point subgroup
$C_G(H)$ of the complement, while the rank of
$G$ is bounded above in terms of
$|H|$ and the rank of
$C_G(H)$. Earlier, such results were known under the stronger assumption that the kernel
$F$ acts on
$G$ fixed-point-freely. As a corollary, for the case where
$G$ is an arbitrary finite group with a Frobenius group
$FH$ of automorphisms of coprime order with kernel
$F$ and complement
$H$, estimates are obtained which are of the form
$|G|\le|C_G(F)|\cdot f(|H|,|C_G(H)|)$ for the order, and of the form $\mathbf r(G)\le\mathbf r(C_G(F))+g(|H|,\mathbf r(C_G(H)))$ for the rank, where
$f$ and
$g$ are some functions of two variables.
Keywords:
finite group, Frobenius group, automorphism, rank, order, $p$-group.
UDC:
512.542 Received: 22.08.2012