依题意可知（n+1）/(a1 +a2/2 +a3/3 +----+ an/n )=1/(n+1) 所以(n+1)^2= a1 +a2/2 +a3/3 +----+ an/n令bn=an/n ,b1=a1=2/H1=4所以(n+1)^2=b1+b2+b3+.+bn--------------令n=n+1所以（n+2)^2=b1+b2+b3+...+bn+bn+1---...