How can I prove this statement ? $ \phi(n) = n/2$ iff $n = 2^k $
I'm thinking n can be decomposed into its prime factors, then I can use multiplicative property of the euler phi function to get the $\phi(n) = \phi(p_1)\cdots\phi(p_n) $. Then use the property $ \phi(p) = p - 1$. But I'm not sure if that's the proper approach for this question.