an - a(n-1)= ln n/(n-1)a(n-1) - a(n-2) = ln (n-1)/(n-2)……a2 - a1 = ln2/1左右相加an-a(n-1)+a(n-1) -……-a1 = ln (1+n)/n + ln n/(n-1)+……ln 2/1 = ln (1+n)/n * … 2/1 = ln nan = 2+ln n
