Step 1: Divide the number into separate digits:
8443 => 8 4 4 3
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 4 = 4
4 to 4 = 0
4 to 3 = 1
3 to 8 = 5
Step 3: Combine the filters to a string:
4 0 1 5 = 4015