The numbers that have 15 as a multiple are 1, 3, 5 and 15. Becasue, 115 = 15; 35 = 15; 5 3 = 15; and 151 = 15. The easiest way to do that is to factor 15 in the prime factors: 15 = 135, and then see the possible combinations, which are 1 15, 35, 5 3 and 15 1. Therefore 15 is multiple of 1, 2, 3 and 15 itself.
