When the number is a square of a Prime number. Of course, it will have a repeated factor, but it will still only have 3 distinct factors. 4, 9, 25, 49, 121 are some examples.
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A factor = a number which can be divided into the given number with no remainder so no, 3 is not a factor of 20
202
It's a perfect square.
Odd. I determined my answer by looking at the number of factors of a square number.
14