42, 105, 56最大公因数 = 7最小公倍数 = 84042 = 2 * 21 = 2 * 3 * 7105 = 3 * 35 = 3 * 5 * 756 = 2 * 28 = 2 * 2 * 14 = 2 * 2 * 2 * 7 = 2^3 * 7最大公因数 = 7最小公倍数 = 840 = 2 * 2 * 2 * 3 * 5 * 7 = 2^3 * 3 * 5 * 7
