Step 1: Divide the number into separate digits:
2685 => 2 6 8 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 6 = 4
6 to 8 = 2
8 to 5 = 3
5 to 2 = 3
Step 3: Combine the filters to a string:
4 2 3 3 = 4233