Only the number 1.
1 +1
Nothing goes into 13 evenly other than 1 and 13, so that means it is a prime number.
The multiples of each number from 1-30.
1 and 53
1, 61.
1, 71.
The number 1.
3 will go into both 15 and 27. 1 will go into any number, so also 1.
Only the number 1.
1 because only 1 can go into it
Only the number 1.