Consider this function.
$$f(n)=\sum_{k=1}^{n}\phi (k)$$
where $\phi (k)$ is the Euler's totient function. I'm wondering are there infinitely many $n$ such that $n\mid f(n)$? For $n\leq 4000$ only solutions are $1, 2, 5, 6, 16, 25, 36, 249, 617, 1296$