I need to prove that
$$\phi(mn) > \phi(m)\phi(n)$$
if $m$ and $n$ have a common factor greater than 1.
I have read up on the case where $m$ and $n$ are relatively prime, then $\phi(mn)=\phi(m)\phi(n)$.
I need to prove that
$$\phi(mn) > \phi(m)\phi(n)$$
if $m$ and $n$ have a common factor greater than 1.
I have read up on the case where $m$ and $n$ are relatively prime, then $\phi(mn)=\phi(m)\phi(n)$.