an=a1+a2/2+a3/3+……+an-1/n-1(n>=2)an+1=a1+a2/2+a3/3+……+an-1/n-1+an/n(n>=2)两式相减：an+1-an=an/n(n>=2)化简变形：an+1/n+1=an/n(n>=2)可以推到：an/n=……=a2/2(n>=2)易求出a2=a1=1/2所以an=n*a2/2=n/4(n>=...