one.
only 1 and 7 can go into 7 evenly.. but 9 and 3 go into 27 evenly
1, 3, 9, 27.
Only the number one (1) goes evenly into both 25 and 27.
3
9.
1 and 9
1, 3, 9.
27 is 3 to the 3rd power, and 64 is 2 to the 6th power, so the only number that goes into both evenly is one (1).
1 and 2
2
6