3/2+13/6+37/12+81/20+151/30+253/42+393/56
=(1+1/2)+(2+1/6)+(3+1/12)+(4+1/20)+(5+1/30)+(6+1/42)+(7+1/56)
=(1+……+7)+[(1-1/2)+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7)+(1/7-1/8)]
=28+1-1/8
=231/8