(2-1)(2+1)(2^2 + 1)(2^4 +1)(2^8 + 1)(2^16 + 1)(2^32 + 1)
=(2^2 -1) (2^2 + 1) (2^4 + 1) (2^8 + 1) (2^16 + 1) (2^32 + 1)
=(2^4 -1) (2^4 + 1) (2^8 + 1) (2^16 + 1) (2^32 + 1)
=2^64 -1
2^1 2^2 2^3 2^4 2^5 2^6 2^7 2^8.2^64
2 4 8 16 32 64 128 256.,...6
2的n次方,当n为为4的整数倍时,2^n的个位数为6
64/4 = 8,所以 2^64 的个位数为 6
2^64 - 1 的个位数为 5