Step 1: Divide the number into separate digits:
8320 => 8 3 2 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 3 = 5
3 to 2 = 1
2 to 0 = 2
0 to 8 = 8
Step 3: Combine the filters to a string:
5 1 2 8 = 5128