How do you find all the generators $(\Bbb Z_{19})^\times$?
I know the generators for $\Bbb Z_n$ is all elements, $a$, where $\gcd(a,n)=1$, so for $\Bbb Z_{19}=\{1,2,\dots, 18\}$ since $19$ is prime.
I am not sure how to do it for $(\Bbb Z_n)^\times.$