Step 1: Divide the number into separate digits:
8675 => 8 6 7 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 6 = 2
6 to 7 = 1
7 to 5 = 2
5 to 8 = 3
Step 3: Combine the filters to a string:
2 1 2 3 = 2123