(2+1)(2²+1)(2^4+1)(2^8+1)+1
=(2-1)(2+1)(2²+1)(2^4+1)(2^8+1)+1
=(2²-1)(2²+1)(2^4+1)(2^8+1)+1
=(2^4-1)(2^4+1)(2^8+1)+1
=(2^8-1)(2^8+1)+1
=2^16-1+1
=65536