252, 504, 756 and so on.
252
Any multiple of 252.
No, they are factors.
126, 252, 378
No, they are factors.
84, 168, 252
Any multiple of 252
252
If that's 9, 14 and 21, the first three common multiples are 126, 252 and 378.
84, 168, 252 and so on.
84, 168, 252
2. Nothing else will work