转化               分母(1)1/1               1/1                (1)(2)1-1/2             1/2                (2)(3)1-1/2+1/3         1/2+1/3            (2,3)(4)1-1/2+1/3-1/4     1/3+1/4            (3,4)(5)                  1/3+1/4+1/5        (3,4,5)(6)                  1/4+1/5+1/6        (4,5,6)(7)                  1/4+1/5+1/6+1/7    (4,5,6,7)(8)                  1/5+1/6+1/7+1/8    (5,6,7,8)
function f(n){  let res = 0;  for (let i = n; i >= Math.floor(n / 2) + 1; i--) {      res += (1 / i);  }  return res;}