Automorphisms of a finite cyclic group
Let
- Prove that the map
is a well-defined automorphism of . - Prove that any automorphism of
has the form for some .
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Let ${\bf Z}_n$ denote the cyclic group of order $n$. Suppose $m\in {\bf N}$ is relatively prime to $n$. Define the function $\mu_m:{\bf Z}_n\to {\bf Z}_n$ by $m[a]_n=[ma]_n$.
\begin{enumerate}[label=\alph*)]
\item Prove that the map $\mu_m$ is a well-defined automorphism of ${\bf Z}_n$.
\item Prove that any automorphism of ${\bf Z}_n$ has the form $\mu_m$ for some $m$.
\end{enumerate}