We simplify this number to two digits, and the digits on the two digits are X and Y respectively. So it can be composed of two digits: a =10 * x+y; B =10 * y+X. You can get it by subtracting two numbers.

A-B =10 * x+y-10 * y-x = 9 * (x-y), that is, if x and y are not equal, then a-b can be divisible by 9. I don't know if you still remember that the characteristic of numbers divisible by 9 is that the sum of digits can be divisible by 9. If it is a two-digit number, it is a two-digit number divisible by 9. We repeat the above proof process until the sum of two digits is one digit, which is 9!

Therefore, the establishment condition of this problem must be more than 2 digits, and all digits cannot be the same.