Themselves and their multiples because 17 and 13 are both prime numbers.
221
Most probably quite a few. However the most obvious is 17*13 = 221.
It is their lowest common multiple which is 221 13 and 17 are both prime numbers
The whole number between 13 and 17 is 15
Nothing goes into 13 evenly other than 1 and 13, so that means it is a prime number.
n + 20 - 17 + 13 - n = 20 - 17 + 13 = 3 + 13 = 16
17
It is 30 because 30-17 = 13
1 and 17 (17 is a prime number).
17 is prime and 68 is 17 times 4, so the number that can go into 17 and 68 is 17.
17.
13