Question 113
Let $\delta(n)$ denote the number of positive divisors of $n$ and let $\phi(n)$ denote the number of non-negative integers less than $n$ and relatively prime to $n$.
Find all positive integers $n$ such that $\delta(n) \cdot \phi(n) = n$.
Find all positive integers $n$ such that $\delta(n) \cdot \phi(n) = n$.