Please write a four-digit number at will. It doesn't matter if the four digits of this number are the same, but they can't be exactly the same, such as111,7777, etc. , should be ruled out. After you write down the number, you should classify it. It does this by rearranging the numbers in descending order. For example, the selected number is 5477, and the sorted number is 7754. The next step is to reverse the obtained number, and then subtract the second number from the first number to find the difference. For this difference, repeat the above steps to get a new difference. Repeat the above steps several times to get 6 174. Let's do the above example from beginning to end: 7754-4577 = 3177 7731377 = 6354 6543-3456 = 3087 8730-0738 = 8352 8532-2352. In short, four digits (except111,2222, ... 9999) will find its final destination-6174 after several transformations. A positive integer, no matter how many digits it is, is called "self-replicating number" if its inverse number is subtracted from the number from the largest number to the smallest number (that is, the number from the smallest number to the largest number), and the difference is still the number of the original number. Obviously, 6 174 is a "self-copied number" because other "self-copied numbers" exist besides 6 174. If 954-459 = 495 987542101245789 = 9750842 1, then 495 and 97508421are also "self-copied numbers".