1/(n+1)+1/(3n+1)>2/(2n+1)1/(n+2)+1/(3n)>2/(2n+1).........1/(2n)+1/(2n+2)>2/(2n+1)1/(2n+1)=1/(2n+1)1/(n+1)+1/(n+2)+....+1/(3n+1)>(2n+1)/(2n+1)=1
