For each positive integer $n$, let $f_1(n)$ be twice the number of positive integer divisors of $n$, and for $j \ge 2$, let $f_j(n) = f_1(f_{j-1}(n))$. Find the number of values of $n \le 50$ for which $f_{50}(n) = 12$.

Let's think step by step and output the final answer within \boxed{}.
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