(2+1)(2^2+1)(2^4+1)……(2^32+1)
=(2-1)(2+1)(2^2+1)(2^4+1)……(2^32+1)
=(2^2-1)(2^2+1).(2^32+1)
=...
=(2^32-1)(2^32+1)
=2^64-1
2^n个位是以2、4、8、6循环
64÷4=16
个位是6-1=5