MYSTERIOUS MAGIC NUMBER 6174 (PLAYING WITH NUMBER)

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 descending and then in ascending 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 and repeat.

The above process, known as Kaprekar's routine, will usually reach its fixed point, 6174, in at most 8 iterations.^[4] Once 6174 is reached, the process will continue yielding 7641 – 1467 = 6174. For example, choose 3524:

5432 – 2345 = 3087

8730 – 0378 = 8352

8532 – 2358 = 6174

7641 – 1467 = 6174

The only four-digit numbers for which Kaprekar's routine does not reach 6174 are repdigits such as 1111, which give the result 0000 after a single iteration. All other four-digit numbers eventually reach 6174 if leading zeros are used to keep the number of digits at 4.

This video features University of Nottingham physics professor Roger Bowley, WATCH THIS VIDEO TO SEE NUMBER MAGIC...... 

SOURCE:
https://en.wikipedia.org/wiki/6174_(number)
https://www.youtube.com/user/numberphile/videos