(1-1/15)+(1-1/35)+(1-1/63)+(1-1/99)+(1-1/143)+(1-1/195)+(1-1/255)+(1-1/323)

(1-1/15)+(1-1/35)+(1-1/63)+(1-1/99)+(1-1/143)+(1-1/195)+(1-1/255)+(1-1/323)
(1-1/15)+(1-1/35)+(1-1/63)+(1-1/99)+(1-1/143)+(1-1/195)+(1-1/255)+(1-1/323)

(1-1/15)+(1-1/35)+(1-1/63)+(1-1/99)+(1-1/143)+(1-1/195)+(1-1/255)+(1-1/323)
(1-1/15)+(1-1/35)+(1-1/63)+(1-1/99)+(1-1/143)+(1-1/195)+(1-1/255)+(1-1/323)
=8-(1/15+1/35+1/63+1/99+1/143+1/195+1/255+1/323)
=8-1/2*[2/(3*5)+2/(5*7)+2/(7*9)+2/(9*11)+2/(11*13)+2/(13*15)+2/(15*17)+2/(17*19)]
=8-1/2*[(1/3-1/5)+1/5-1/7+1/7-1/9+1/9-1/11+1/11-1/13+1/13-1/15+1/15-1/17+1/17-1/19]
=8-1/2(1/3-1/19)=8-8/57=7又49/57