no numbers!
Nothing can go evenly into 21 or 17. They are both odd numbers and therefore cannot be evenly divided.
Each of these numbers will go evenly into 75: 1, 3, 5, 15, 25, 75.
255
1,3,5,9,15,45
60.5
1,2,3,6,7
11,6,1,2,33
n
2,4,7
1,2,4,8,16,32
6 of them go in evenly.