bn=2^n-1
那么
1/b1+1/b2+1/b3+……+1/bn
=1/1+1/3+...>1
怎么会小于1/2
题目错了把
1/b1+1/b2+1/b3+……+1/bn
=1/1+1/3+...+1/(2^n-1)
<1/1+1/2+...+1/2^(n-1)
=2-1/2^(n-1)
<2