Euler's totient function

Quote:

Originally Posted by Rafael Almeida

Hi all again,

Now the problem is with Euler's Function. See:

1. Find all positive and integer $n$ such that $\varphi(n) = pq$ , where p and q are prime.
2. Find all positive numbers $n$ such that $\varphi(n) = 8$

How do I approach these? Any tips are welcome.

Thanks in advance,

Write $n=p_1^{a_1}...p_k^{a_k}$ and now apply formula for $\phi (n)$ .
After that compare sides and see what $n$ got to be.

Also for (1) it seems that $p,q$ are odd primes because $\phi(n) = 14$ has no solutions.