(1+2)*(1+4)*(1+16)*(1+256)
=(1-2)(1+2)*(1+4)*(1+16)*(1+256)/(1-2)
=(1-4)*(1+4)*(1+16)*(1+256)/(1-2)
=(1-16)*(1+16)*(1+256)/(1-2)
=(1-256)*(1+256)/(1-2)
=(1*1-256*256)/(-1)
=256*256-1
=65535
=(1-2)(1+2)(1+4)(1+16)(1+256)/(1-2)
=(1-4)(1+4)(1+16)(1+256)/(-1)
=(1-16)(1+16)(1+256)/(-1)
=(1-256)(1+256)/(-1)
=(1-2^16)/(-1)
=2^16-1