Find the number of primitive roots in $\displaystyle \mathbb{Z}_{101}$, $\displaystyle \mathbb{Z}_{12}$.

I cannot find an example from my lecture notes about primitive roots in $\displaystyle \mathbb{Z}_n$. What is the definition of primitive roots in $\displaystyle \mathbb{Z}_n$?

The answers are 40 and none respectively.