Step 1: Divide the number into separate digits:
5875 => 5 8 7 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 8 = 3
8 to 7 = 1
7 to 5 = 2
5 to 5 = 0
Step 3: Combine the filters to a string:
3 1 2 0 = 3120