Σ(n=1 to ∞)［1/(n+1)-1/(n+3))］
=lim_{a->inf}sun(1/(n+1)-1/(n+3),n=1,n=a)
=lim_{a->inf}((1/2-1/4)+(1/3-1/5)+...+(1/a-1/(a+2))+(1/(a+1)-1/(a+3))).