1, the difference between any number with two digits or more and the new number formed by the inversion of this number can be divisible by 9.

2. For a positive integer, if it is odd, multiply it by three plus one; If it is an even number, divide by two; In this way, you can always get the cycle of 1, 4,2, 1.

3. For any three-digit number, subtract the number obtained from the number arranged from the smallest to the largest, continue this process, and finally get 495.