How many natural numbers less than 1000 have exactly three distinct positive integer divisors?

This seems tougher than it really  is

Note....that every  non-square natural number will have an even number of divisors

For instance.....the divisors  of 8  are  1  2  4  8

However....the perfect squares always  have an odd number of divisors

For instance....the divsors of 16  are  1  2  4  8  and 16

And  the perfect squares  which have prime square roots  will  only  have 3 divisors

For instance...9   has a square root of 3 which is prime....so...it will only have 3 divisors  ⇒ 1, 3 and 9

So...the squares  < 1000  which have prime square roots are

4            289

9            361

25          529

49          841

121        961

169

So...11  natural numbers < 1000   have  only 3 divisors