1+1/1+2+1/1+2+3+…+1/1+2+3+…+n =1+1/3+1/6+.+1/(1+n)n/2=1+1/3+1/6+.2/(1+n)n=2[1/2+1/6+1/12+.+1/n(n+1)]=2[1/1*2+1/2*3+1/3*4+.+1/n(n+1)]=2[1-1/2+1/2-1/3+1/3-1/4+...1/n-1/(n+1)]=2[1-1/(n+1)]=2*n/(n+1)=2n...