Step 1: Divide the number into separate digits:
5328 => 5 3 2 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 3 = 2
3 to 2 = 1
2 to 8 = 6
8 to 5 = 3
Step 3: Combine the filters to a string:
2 1 6 3 = 2163