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Let $p\ge 2$ be prime.
An integer $a$ is called a primitive root mod $p$ if there is no positive integer $h$ strictly smaller than $p-1$ with $a^h\equiv 1$ mod $p$.
Which of the following is true?
There are no primitive roots mod $3$.
If $a\not\equiv0$ mod $p$ and $h$ is the smallest positive integer with $a^h\equiv 1$ mod $p$, then $h$ divides $p-1$.
There are $3$ primitive roots mod $5$.
$3$ is not a primitive root mod $7$.
If $a$ is a primitive root mod $p$, then so is $a^k$, for all $k=1,\ldots,p-1$.