Hello from MrBillDoesMath!
Answer: 23
Discussion:
We only need to check primes less that the square root of 576, which is about 23.98. As 23 is a prime number, it is the answer to the question.
Another way of looking at this: the primes less than or equal to 23
(23*23 = 529)
2, 3, 5,7,11,13,17,19,23
The greatest prime in the list is 23
Thank you,
MrB