Set C contains all counting numbers less than 20

[math_celebrity]

C = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19}

Notice, we do not include 20 since it said less than, and not less than or equal to.