A=(2-1)(2+1)*...*(2^256+1)+1
=(2^2-1)(2^2+1)*...*(2^256+1)+1
=(2^4-1)(2^4+1)*...*(2^256+1)+1
=(2^8-1)(2^8+1)(2^16+1)(2^32+1)*....*(2^256+1)+1
=(2^16-1)(2^16+1)*....*(2^256+1)+1
=(2^32-1)(2^32+1)*...*(2^256+1)+1
=(2^64-1)(2^64+1)(2^128+1)(2^256+1)+1
=(2^128-1)(2^128+1)(2^256+1)+1
=(2^256-1)(2^256+1)+1
=2^512