Step 1: Divide the number into separate digits:
8574 => 8 5 7 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 5 = 3
5 to 7 = 2
7 to 4 = 3
4 to 8 = 4
Step 3: Combine the filters to a string:
3 2 3 4 = 3234