同构数，又称为自守数
若M的n次方的尾部是M则称M是n阶同构数(或n阶自守数)
若M的2次方的尾部是M则称M是2阶同构数(或2阶自守数)
如5^2=25;6^2=36等
二阶同构数只有两族，即个位是5和个位是6的两族！

class TongGou 

{

         public static void istonggou(int n)

         {

                   int x;

                   x = (n * n) % 10;

                   if(x == n)

                            System.out.println("是同构数");

                   else

                            System.out.println("不是同构数");

         }

       public static void main(String[] args) 

         {

                   istonggou(5);

         }

}