（1/8+1/24+1/48+1/80+1/120+1/168+1/224)*64=（1/2*4+1/4*6+1/6*8+1/8*10+1/10*12+1/12*14+1/14*16）*64=1/2*(1/2-1/4+1/4-1/6+.+1/14-1/16)*64=32(1/2-1/16)=16-2=14