Interesting number - 6174

If you take any 4 digit number (that is not a repeating number like 1111), re-arrange the digits so that you have the highest possible value, re-arrange them again to get the smallest value with those digits, subtract the smaller one from the bigger one and repeat the process...then you will (within 7 tries) get to the answer of 6174. That answer will repeat at that point.

Example with the number 5014:

Largest arrangement		Smallest Arrangement		Answer
5410		0145		5265
6652		2556		4096
9640		0469		9171
9711		1179		8532
8532		2358		6174
7641		1467		6174 (repeats)

So, 5014 took 5 tries. There appears to be no known reason for this -- it's just a strange occurrence for 4 digit numbers. A similar thing happens with 3 digit numbers, but the final answer is different.

http://plus.maths.org/issue38/features/nishiyama/index.html