# Prove that for every odd prime number $p$ there is a non-commutative group of order $p^3$ such that…

Prove that for every odd prime number $p$ there is a non-commutative group of order $p^3$ such that $a^p = e$, $\forall a \in G$.

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 hint: can you write down a non-trivial map from $\mathbb{Z}/p$ to Aut$((\mathbb{Z}/p)^2)$? – countinghaus Dec 9 '12 at 7:25

Note that $\text{Aut}(\mathbb{Z}_p^2)\cong\text{GL}_2(\mathbb{F}_p)$, and since $|\text{GL}_2(\mathbb{F}_p)|=(p^2-1)(p^2-p)$ we see in particular, $p\mid |\text{Aut}(\mathbb{Z}_p)|$. Thus, there exists a non-trivial homomorphism $\varphi:\mathbb{Z}_p\to\text{Aut}(\mathbb{Z}_p^2)$. Consider then $G=\mathbb{Z}_p^2\rtimes_\varphi\mathbb{Z}_p$. Prove that this is the group you seek.
 How exactly is $\text{GL}_2(\mathbb{F}_p)$ defined? We haven't learned about it. However, I think I can try to prove that the group $G$ that you provided is the group I seek. – chubbycantorset Dec 9 '12 at 7:30 $2 \times 2$ matrices with nonzero determinant over $\mathbb{F}_p$, who you may know by his psuedonym $\mathbb{Z}_p$ or $\mathbb{Z}/p\mathbb{Z}$. The $\mathbb{F}$ is to emphasize that it is a field. – andybenji Dec 9 '12 at 7:31 It's just $2\times 2$ invertible matrices over the field of $p$ elements. – Alex Youcis Dec 9 '12 at 7:32 And how exactly does it imply that there exists a nontrivial homomorphism $\varphi:\mathbb{Z}_p\to\text{Aut}(\mathbb{Z}_p^2)$ ? – chubbycantorset Dec 9 '12 at 7:39 Because you can just send the generator of $\mathbb{Z}_p$ to the element an element of order $p$ in $\text{Aut}(\mathbb{Z}_p^2)$--one exists by Cauchy's theorem. – Alex Youcis Dec 9 '12 at 7:40