21, 42 and 63
If that's 9, 14 and 21, the first three common multiples are 126, 252 and 378.
21
42, 84, 126
63, 126, 189
84, 168, 252
63, 126, 189
7, 14, 21
63, 126, 189
126, 252, 378
126, 252, 378 and so on.
Any multiple of 21.
LCM(9, 21) = 63 so the numbers are 63, 63*2 and 63*3.