Kaprekar's constant - 6174
In 1949, an Indian mathematician, Dr. Kaprekar, discovered an amazing property of the number 6174, which was named the Kaprekar constant.
The magician behind 6174 discovered by Kaprekar have following rule explained in the next image.
This routine doesn't reach the number 6174 only if you use repdigits such as 1111 or 5555