那个数是 2^9 = 512为什么？？？need 9 times to 去掉 2^9 and all other numbers at most 8times1 2 345 6 7 8 9 10 11 12 13 14 152 4 6 8 10 12 14--> 2m4 8 12 --> 4n 8 --> 8k