原式
=1 + 150/15 + 150/35 + 150/63 + 150/99 + 150/143
=1 + 150*(1/15 + 1/35 + 1/63 + 1/99 + 1/143)
=1 + 150*(1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + 1/9 - 1/11 + 1/11 -1/13)/2
=1 + 75*(1/3 - 1/13)
=1 + 250/13
=20 + 3/13