(a+1)(a^2+1)(a^4+1)(a^8+1)(a^16+1)

(a+1)(a^2+1)(a^4+1)(a^8+1)(a^16+1)
=(a-1)[(a+1)(a^2+1)(a^4+1)(a^8+1)(a^16+1)]/(a-1)
=[a^2-1)(a^2+1)(a^4+1)(a^8+1)(a^16+1)]/(a-1)
=[(a^4-1)(a^4+1)(a^8+1)(a^16+1)]/(a-1)
=[(a^8-1)(a^8+1)(a^16+1)]/(a-1)
=[(a^16-1)(a^16+1)]/(a-1)
=(a^32-1)/(a-1)
为什么要除以（a-1）