After 6, all numbers divisible by 3 can be ordered. After 26, all numbers divisible by 3 when subtracted by 20 can be obtained. After 46, all numbers divisible by 3 when subtracted by 40 can be obtained. After 46, all numbers fit into one of these 3 categories, so all numbers can be obtained. 43 is the last number that doesn't fall into one of these categories (44 = 20 + 6 * 4, 45 = 6 * 6 + 9).