The answer is 49.
25
81
We need to know what number the square is a factor of.
Just 1.
36
The greatest perfect square is 36.
17 is a prime number. Its only factors are 1 and 7. Since 1 is a perfect square, it is the answer to the question.
25
9
36
One.
idl
81
64
650 has no factor that is a perfect square, other than 1.
16
No.