The number $100$ has four perfect square divisors, namely $1,$ $4,$ $25,$ and $100.$ What is the smallest positive integer that has exactly $2$ perfect square divisors?
So we can see that every number has at least one square divisor(except 0) which is 1.
Now we can see that it has to be 4 because it is divisble by 1^2 and 2^2
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