D (400) = {1, 2, 4, 5, 8, 10, 16, 20, 25, 40, 50, 80, 100, 200, 400}
D (150) = {1, 2, 3, 5, 6, 10, 15, 25, 30, 50, 75, 150}
mdc (400, 150) = 50
D (30) = {1, 2, 3, 5, 6, 10,15, 30}
D (45) = {1, 3, 5, 9, 15, 45}
D (28) = {1, 2, 4, 7, 14, 28}
mdc (30, 45, 28) = 1
