Step 1: Divide the number into separate digits:
8459 => 8 4 5 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 4 = 4
4 to 5 = 1
5 to 9 = 4
9 to 8 = 1
Step 3: Combine the filters to a string:
4 1 4 1 = 4141