Q:

Number theory problem exercise?

Find all natural numbers $N$  so that $\varphi(N)=24$ where $\varphi$  is Euler's function.

A:

Hint - if a prime $p$ is a factor of $N$ then you should be able to show that $p-1$ is a factor of $\varphi(n)$ and use this to identify the possible prime factors of $N$.

