补充一点:筛除2,3,5,7,11,13,17,19的倍数含量。得
500(1-1/2)(1-1/3)(1-1/5)(1-1/7)(1-1/11)(1-1/13)(1-1/17)(1-1/19)=85.512011211
加强筛除2,3,5,7,11,13,17,19的倍数含,过程是用4/7,13/36,1/3,1/5,1/7,1/11,1/13,1/17,依次代替1/2,1/3,1/5,1/7,1/11,1/13,1/17,1/19,得
500(1-4/7)(1-13/36)(1-1/3)(1-1/5)(1-1/7)(1-1/11)(1-1/13)(1-1/17)
=49.429562036
而2,3,5,7,11,13,17,19按倍数筛去了,还实际有87个 |