1+1/2+1/4+1/8+...+1/64
=1+(1-1/2)+(1/2-1/4)+(1/4-1/8)+...+(1/32-1/64)
=1+1-1/2+1/2-1/4+1/4-1/8+...+1/32-1/64
=1+1-1/64
=2-1/64
=127/64