To work with us, answer one qualifying question and enter your email address.

- Take any four-digit number, using at least two different digits. (Leading zeros are allowed.)
- Arrange the digits in descending and then in ascending order to get two four-digit numbers, adding leading zeros if necessary.
- Subtract the smaller number from the bigger number.
- If you get the same number that you used in step 2, then enter it below as your answer. Otherwise, go back to step 2 with the number you got in step 3.