Kaprekar’s constant : ‘6174 .. is notable for the following property: Take any four-digit number, using at least two different digits. (Leading zeros are allowed.); Arrange the digits in ascending and then in descending order to get two four-digit numbers, adding leading zeros if necessary; Subtract the smaller number from the bigger number; Go back to step 2. The process will reach 6174 in at most 7 iterations’

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