9.
The number one.
1, 3, 5, 9, 15, 25, 27, 45, 75, 135, 225, 675
9
1, 3, 5, 9, 15, 45.
3
1, 3, 5, 9, 15, 27, 45, 135.
One.
One.
1, 3, 5, 9, 15, 25, 45, 75, 225.
There is no number that goes into all three of those numbers.
1, 3, 5, 9, 15, 45.
1 and 3.