2 * 2 * 5 = 20,

делители числа 20:   1, 2, 4, 10, 20,

3 * 5 * 7 = 105,

делители числа 105:   1, 3, 5, 7, 15, 21, 35, 105,

(2 * 2 * 5) * (3 * 5 * 7) = 20 * 105 = 2100,

делители числа 2100:  1, 2, 3, 4, 5, 6, 7, 10, 12, 15, 20, 25, 30, 35, 40, 42, 50, 60, 70, 84, 100, 105, 175, 210, 300, 350, 420, 525, 700, 1050, 2100