原式=(1-1/2)(1+1/2)(1+1/4)(1+1/16)(1+1/256)/(1-1/2)=(1-1/4)(1+1/4)(1+1/16)(1+1/256)/(1-1/2)=(1-1/16)(1+1/16)(1+1/256)/(1-1/2)=(1-1/256)(1+1/256)/(1-1/2)=(1-1/65536)/(1/2)=65535/65536×2=65535/32768
上式乘(1-1/2)/(1+1/2)得(1-1/256^2)/(1-1/2)