m是奇数，且m>=3

=>m可以用表达式2n-1，n>=2

=>m²-1 = (2n-1)²-1

=>m²-1 = 4n²-4n+1-1

=>m²-1 = 4n²-4n

=>m²-1 = 4n(n-1)

=>m²-1 = 4*奇数*偶数

由于n>=2，则4*奇数*偶数必然能被8整除

=>m²-1必然能被8整除

=>m(m²-1)必然也能被8整除