mem·o·ry·less·ness

The magic that magic numbers do is all too often black. They hold special significance for terrestrial mammals with hands and watches, but they mean nothing to streptococcus or the value of Google.

6174 is known as Kaprekar’s constant after the Indian mathematician D. R. Kaprekar. This number is notable for the following property:

1. Take any four-digit number, using at least two different digits. (Leading zeros are allowed.)
2. Arrange the digits in ascending and then in descending order to get two four-digit numbers, adding leading zeros if necessary.
3. Subtract the smaller number from the bigger number.
4. Go back to step 2.

The above process, known as Kaprekar’s routine, will always reach 6174 in at most 7 iterations. (via joshad)

 (via bestofwikipedia)