Multiples of 3

3, 6, 9, 12, 15, 18, 21, 24, 27, 30

What is the pattern?

0+3, 0+6, 0+9, 1+2, 1+5, 1+8, 2+1, 2+4, 2+7, 3+0

3, 6, 9, 3, 6, 9, 3, 6, 9, 3

The sum of the digits follows the pattern 3, 6, 9.