Step 1: Divide the number into separate digits:
8568 => 8 5 6 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 5 = 3
5 to 6 = 1
6 to 8 = 2
8 to 8 = 0
Step 3: Combine the filters to a string:
3 1 2 0 = 3120