30=6*5 so 6 is the greatest factor of 30. Numbers with 6 as a factor can be represented by 6n where n is an integer. So that means any multiple of 6 up to 6*5, i. e., 6, 12, 18, 24. Then we continue: 36, 42, 48, 54. We can't include 60 for the same reason as we exclude 30, because 30 would be the GCF. So we continue 66, 72, 78, 84, avoiding multiples of 5.