Question 45
Find all positive integers $n$ such that
$$
d(n) \mid 2^{\sigma(n)} - 1.
$$
(Where $d(n)$ and $\sigma(n)$ are the total number and the sum of positive divisors of $n$.)
$$
d(n) \mid 2^{\sigma(n)} - 1.
$$
(Where $d(n)$ and $\sigma(n)$ are the total number and the sum of positive divisors of $n$.)