The above process, known as Kaprekar's routine, will always reach its fixed point, 6174, in at most 7 iterations. Once 6174 is reached, the process will continue yielding 7641 – 1467 = 6174. For example, choose 3524:

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.

Note that there can be analogous fixed points for digit lengths other than four, for instance if we use 3-digit numbers then most sequences will terminate in the value 495. Sometimes these numbers (495, 6174, and their counterparts in other digit lengths or in bases other than 10) are called "Kaprekar constants".

6174 is a Harshad number, since it is divided by the sum of its digits:

6174 = (1 + 6 + 7 + 4) × 343.

6174 is a 7-smooth number, i. e. all its prime factors are not greater than 7.

6174 is a practical number , because an arbitrary number less than 6174 can be represented as a sum of various factors of the number 6174. This is a not uncommon property, and the nearest neighboring practical numbers are 6160, 6162, 6180, 6188.

6174 can be written as the sum of the first three degrees of the natural number 18:

18³ + 18² + 18 = 5832 + 324 + 18 = 6174.

The sum of squares of the prime factors of 6174 is an exact square:

2² + 3² + 3² + 7² + 7² + 7² = 4 + 9 + 9 + 49 + 49 + 49 = 169 = 13².

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