Do all square numbers have exactly 3 factors?

No. 81=9*9=3*27=1*81

81 has 5 factors and is a square number.

36=6*6=3*12=1*36=2*18=4*9

36 has 9 factors and is a square number.

This doesn't mean that no square numbers have exactly 3 factors though, because:

9=3*3=1*9

9 has 3 factors and is a square number.

4=2*2=1*4

4 has 3 factors and is a square number.

All square numbers have an odd number of factors though (because they have a whole number which multiplies by itself to get the number).

Factors are whole numbers only, and not decimals.

Hope this helps :)