How often is Euler's totient a perfect power? (Q1634410)

In the paper under review, the author studies portion of perfect \(k\)th power values of the Euler's totient. Letting \[ L(x)=e^{(\log x)(\log\log\log x)/\log\log x}, \] he proves that as \(x\to\infty\), the number of \(n\leq x\) for which \(\varphi(n)\) is squarefull is at most \(x/L(x)^{1+o(1)}\). He shows conditionally that the number of \(n\leq x\) for which \(\varphi(n)\) is a \(k\)th power (\(k\geq 2\) is a fixed integer) is at least \(x/L(x)^{1+o(1)}\).