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Old 08-26-2016, 10:40 PM
Indistinguishable Indistinguishable is offline
Join Date: Apr 2007
Posts: 10,525
Speaking of four-digit numbers and constant functions, here's a trick:

Take any four digit number whose digits aren't all the same (e.g., 7274), rearrange its four digits into order (e.g., 2477), and subtract this from its reverse (e.g., 7742 - 2477 = 5265).

Keep repeating this process till you get the same value twice in a row (so, in this example, 5265 then becomes 6552 - 2556 = 3996; this in turn becomes 9963 - 3699 = 6264; and one can continue in this fashion a couple more times before getting a repeat).

What value did you get at that point? It'll always be the same: 6174.

Last edited by Indistinguishable; 08-26-2016 at 10:44 PM.