Step 1: Divide the number into separate digits:
8523 => 8 5 2 3
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 5 = 3
5 to 2 = 3
2 to 3 = 1
3 to 8 = 5
Step 3: Combine the filters to a string:
3 3 1 5 = 3315