1/6+1/12+1/20+1/30+....1/9900=(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+....+(1/99-1/100)=1/2-1/3+1/3-1/4+1/4-1/5+.....1/99-1/100=1/2-1/100=49/10099-2+1=98第98个数
