@divisors = grep { $number % $_ == 0 } 1 .. sqrt($number);
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I think you are thinking of prime factorization here. You can stop there to determine primeness but not to determine all factors.

You somehow miss the second line of my optimized solution. It adds the other half of the divisors. :-)

push @divisors, map {$number == $_*$_ ? () : $number/$_} reverse @divi
+sors;
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For every divisor above the square root, there is a corresponding divisor below the square root. Symmetrical optimization. :-)