Least common multiple

The least common multiple (LCM) of two numbers is the smallest number that is a multiple of both. The multiples of 4 are 4, 8, 12, 16, ...; the multiples of 6 are 6, 12, 18, .... The first value in both lists is 12, so the LCM is 12.

The two lists of multiples always meet eventually, because their product is a multiple of both. The LCM is the first place they meet.