### PRIZE PUZZLE FOR NOVEMBER 2005

#### A SPECIAL NUMBER

What 4-figure number is equal to the difference between the same number ordered with descending digits and the same number ordered with ascending digits?

What does this mean? Here is an example. Let 7385 be a trial number. When ordered with descending digits it becomes 8753. When ordered with ascending digits it is 3578. The difference is 8753 - 3578 = 5175. 5175 is not equal to our trial number, 7385, so it is not the answer but that is the method.

I suggest that if it does not work out with your first trial number, continue doing this process on the number you get. Logically, you will either succeed or you will go round in circles! To be more encouraging, actually, you will not go round in circles but will arrive at the one and only true unique answer within a few trial attempts. (Note: there is a trivial answer of 0000 but I don't want that!)

Answer: 6174

7641 - 1467 = 6174

This is the number you eventually end up with if you keep repeating the operation described above. It is thus a very special number. You could use it as your PIN number for bank cards, etc. (Well, you could, if I hadn't mentioned it!)

Only two answers were received so there was no draw this month.

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