Step 1: Divide the number into separate digits:
9144 => 9 1 4 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 1 = 8
1 to 4 = 3
4 to 4 = 0
4 to 9 = 5
Step 3: Combine the filters to a string:
8 3 0 5 = 8305