(2+1)(2^2+1)(2^4+1)┄(2^2N+1)
=(2-1)(2+1)(2^2+1)(2^4+1)┄(2^2N+1)
=(2^2-1)(2^2+1)(2^4+1)┄(2^2N+1)
=(2^4-1)(2^4+1)...(2^2N+1)
...
=2^4N-1.
(2+1)(2^2+1)(2^4+1)┄(2^2N+1)
=(2-1)(2+1)(2^2+1)(2^4+1)┄(2^2N+1)
=(2^2-1)(2^2+1)(2^4+1)┄(2^2N+1)
=(2^4-1)(2^4+1)...(2^2N+1)
...
=2^4N-1.