平方差
(a+1)(a-1)(a^2+1)(a^4+1)(a^8+1)(a^16+1)
=(a^2-1)(a^2+1)(a^4+1)(a^8+1)(a^16+1)
=(a^4-1)(a^4+1)(a^8+1)(a^16+1)
=(a^8-1)(a^8+1)(a^16+1)
=(a^16-1)(a^16+1)
=a^32-1