For a positive integer $n$, let $D(n) =$ number of positive integer divisors of $n$. For example, $D(6) = 4$ because 6 has four divisors, namely $1, 2, 3$ and $6$. Find the number of $n \leq 60$ such that $D(n) = 6$.
For a positive integer $n$, let $D(n) =$ number of positive integer divisors of $n$. For example, $D(6) = 4$ because 6 has four divisors, namely $1, 2, 3$ and $6$. Find the number of $n \leq 60$ such that $D(n) = 6$.