14. The sum of the squares of two certain prime numbers ends with the digit 9. Find all such prime numbers.
14. Since the sum of two addends is an odd number (ending in the digit 9), one addend is even, and the other is odd. Since the parity of a square and its base is the same, one of the two prime numbers is even, and the other is odd. But there is only one even prime number - 2, so its square is 4, which means the square of the second prime number ends in the digit 5. If a square ends in the digit 5, then its base also ends in the digit 5. Among prime numbers ending in the digit 5, there are no numbers other than 5 itself. Therefore, the problem has one solution: 2 and 5.