Step 1: Divide the number into separate digits:
8631 => 8 6 3 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 6 = 2
6 to 3 = 3
3 to 1 = 2
1 to 8 = 7
Step 3: Combine the filters to a string:
2 3 2 7 = 2327