(7+1)(7^2+1)(7^4+1)(7^8+1)(7^16+1)
=(1/6)(7-1)(7+1)(7^2+1)(7^4+1)(7^8+1)(7^16+1)
=(1/6)(7^2-1)(7^2+1)(7^4+1)(7^8+1)(7^16+1)
=(1/6)(7^4-1)(7^4+1)(7^8+1)(7^16+1)
=(1/6)(7^8-1)(7^8+1)(7^16+1)
=(1/6)(7^16-1)(7^16+1)
=(7^32-1)/6
原式乘(7-1)/(7-1)
=(7-1)(7+1)(7^2+1)(7^4+1)(7^8+1)(7^16+1)/(7-1)
=(7^2-1)(7^2+1)(7^4+1)(7^8+1)(7^16+1)/(7-1)
=(7^16-1)/6