If we assume any three digit number (the number should not repeat again in those three digits) and rearrange it in descending order, and deduct the ascending order of the same number, the resultant number should again follow the same steps again. We will end up finishing with 495 beyond which we will not be able to proceed. Let us assume for example 193 as a three digit number. Descending order is 931 and ascending order is 139. If we deduct 139 from 931, the answer is 792. Rearranged in descending order and ascending order again it is 972-279=693. We do this again, it is 963-369=594. We do this again, it is 954-459=495. If you continue any further, the result will stop at 495. You can try any 3 digit number, the end result will stop at 495 beyond which you can't proceed and if you do, it will again give you 495. That is what is so special about this number.