(2n+1)^2-(2n-1)
=4n^2+4n+1-(4n^2-4n+1)
=4n^2+4n+1-4n^2+4n-1
=4n+4n
=8n
因为n为整数
所以8n为8的倍数
所以两奇数平方差是8的倍数