Cool Trick w/ Numbers

[Savy]

Surely you mean 9 fails? unless you're counting 0000 as a 4 digit number.

edit - It's quite interesting that the original operation is actually very restrictive in itself so we aren't really looking at anywhere near 9999 possible numbers due to the fact that 1342 is the same as 4213, etc.

It'd be interesting to see how many numbers churn out 6174 exactly and how many churn out a variation of it.

edit 2 - ignore this link if you actually want to solve it for yourself. Has interesting things 2,3,5,6,etc digit numbers too though and I found the very last big quite interesting too.

http://plus.maths.org/content/mysterious-number-6174

I'd be interested to see if 5 and 7 digit numbers always ended up simplifying down to 9 too, like two digit numbers do.