Step 1: Divide the number into separate digits:
6222 => 6 2 2 2
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 2 = 4
2 to 2 = 0
2 to 2 = 0
2 to 6 = 4
Step 3: Combine the filters to a string:
4 0 0 4 = 4004