A number $n$ is written on a blackboard. In one turn, Albert may choose a divisor $d$ of the number $k$ written on the board and replace $k$ by $k – d$. He wishes to change the number to $1$ in the least possible number of moves; call this number $f(n)$.
For how many integers $n < 1000$ is $2^{f(n) – 1} \leq n$?