The Kaprekar routine can be extended to other number lengths.
For 3 digits its 495. For 1, 2, 5, 6 and 7 digit numbers the Kaprekar's constant doesn't exist.
For six digits two kernel values exist. 549945, 631764
For eight digits again two kernel values 63317664, 97508421
For 8 digits it is 97508421, for 9 digits, 864197532, and for 10 digits, 9753086421
The case of six & 8 digits it cannot be saud that these are Kaprekar constants as two numbers exist.
This was mentioned in one of the books by Martin Gardner.