On Automorphisms of Finite $p$-groups

The power graph of a group is the graph whose vertex set is the set of nontrivial elements of group, two elements being adjacent if one is a power of the other. We introduce some way for find the automorphism groups of some graphs. As an application We describe the full automorphism group of the power graph of all finite groups. Also we obtain the full automorphism group of power graph of abelian, homocyclic and nilpotent groups

Let $p$ be a prime. We construct a function $f$ on the natural numbers such that $f(x) \to \infty$ as $x \to \infty$ and $k_{p}(G)+k_{p'}(G)\geq f(|G|)$ for all finite groups $G$. Here $k_{p}(G)$ denotes the number of conjugacy classes of nontrivial $p$-elements in $G$ and $k_{p'}(G)$ denotes the number of conjugacy classes of elements of $G$ whose orders are coprime to $p$. This is a variation of an old theorem of Landau and is used to prove the following: There exists a num...

We give elementary proofs of the following two theorems on automorphisms of a finite group G: (1) An automorphism of G is inner if and only if it extends to an automorphism of every finite group containing G. (2) There exists a finite group, whose outer automorphism group is isomorphic to G. The first theorem was proved by Pettet using a graph-theoretical construction of Heineken-Liebeck. A Lie-theoretical proof of the second theorem was sketched by Cornulier in a MathOverflo...

We characterize finite $p$-groups $G$ of order up to $p^7$ for which the group of central automorphisms fixing the center element-wise is of minimum possibe order.

Let $p$ be a prime and let $P$ be a Sylow $p$-subgroup of a finite nonabelian group $G$. Let $bcl(G)$ be the size of the largest conjugacy class of the group $G$. We show that $|P/O_p(G)| < bcl(G)$ if $G$ is not abelian.

Let $\psi$ be a permutation of a finite set $X$. We define $\lambda(\psi)$ to be the largest fraction of elements of $X$ lying on a single cycle of $\psi$. For a finite group $G$, we define $\lambda(G)$ to be the maximum among the values $\lambda(\alpha)$, where $\alpha$ runs through the automorphisms of $G$. In this paper, we develop tools to deal with questions related to $\lambda$-values of finite groups and of their automorphisms. As a consequence, we will be able to give...

Let $G$ be a finite group minimally generated by $d(G)$ elements and $\Aut_c(G)$ denote the group of all (conjugacy) class-preserving automorphisms of $G$. Continuing our work [Class preserving automorphisms of finite $p$-groups, J. London Math. Soc. \textbf{75(3)} (2007), 755-772], we study finite $p$-groups $G$ such that $|\Aut_c(G)| = |\gamma_2(G)|^{d(G)}$, where $\gamma_2(G)$ denotes the commutator subgroup of $G$. If $G$ is such a $p$-group of class $2$, then we show tha...

Every finite group whose order is divisible by a prime $p$ has at least $2 \sqrt{p-1}$ conjugacy classes.

A longstanding conjecture asserts that every finite non-abelian $p$-group has a non-inner automorphism of order $p$. In this paper, we settle the conjecture for a finite $p$-group $G$, $p$ an odd prime, of nilpotence class $n$ with $\mbox{exp}(\gamma_{n-1}(G))=p$ and $|\gamma_n(G)|=p,$ where $\gamma_n(G)$ is the $n$th term in the lower central series. As a consequence, we give a short, quite elementary and derivation free proof of the main result of Abdollahi et al. [J. Group...

Let $G$ be a finite group and assume $p$ is a prime dividing the order of $G$. Suppose for any such $p$, that every two abelian $p$-subgroups of $G$ of equal order are conjugate. The structure of such a group $G$ has been settled in this article.