Calculate LCM: Finding the Least Common Multiple of 3 and 7

To find the least common multiple (LCM) of the numbers 3 and 7, we will list the multiples of each number and find the smallest multiple they have in common.

Multiples of 3: $3, 6, 9, 12, 15, 18, 21, \ldots$

Multiples of 7: $7, 14, 21, 28, \ldots$

The smallest common multiple is $21$.