Find all odd integers $n$ for which $\frac{2^{\phi (n)}-1}{n}$ is a perfect square.
Problem
Source: 2008 Brazim IMO TST 3.4
Tags: number theory, phi function, Euler s Phi Function, Perfect Squares
Source: 2008 Brazim IMO TST 3.4
Tags: number theory, phi function, Euler s Phi Function, Perfect Squares
Find all odd integers $n$ for which $\frac{2^{\phi (n)}-1}{n}$ is a perfect square.