15 = 5 * 3
20 = 5 * 2 * 2
НОД (15 ; 20) = 5
42 = 2 * 7 * 3
56 = 2 * 7 * 2 * 2
НОД (42 ; 56) = 2 * 7 = 14
К(3) = {3, 6, 9, 12, 15, 18...}
К(5) = {5, 10, 15, 20...}
НОК (3 ; 5) = 15
К(4) = {4, 8, 12, 16, 20, 24, 28, 32, 36..}
К(9) = {9, 18, 27, 36, 45...}
НОК (4 ; 9) = 36