3, 6, 9, 12, 15, 18, 21.
21, 42 and 63
Multiples of 6: 12, 18, 24 Multiples of 7: 14, 21, 28
42 of them.
Any multiple of 21.
If that's 9, 14 and 21, the first three common multiples are 126, 252 and 378.
21, 42, 63, 84.
7, 14, 21
21, 42, 63.
3,6,9,12,15,18,21,24
22, 44, 66
21
63, 126 and 189