这题利用了平方差公式。原式=(7-1)(7+1)(7^2+1)...(7^32+1)=(7^2-1)(7^2+1)...(7^32+1)=(7^4-1)(7^4+1)...(7^32+1)=...=(7^32-1)(7^32+1)=7^64 - 1
