Step 1: Divide the number into separate digits:
5541 => 5 5 4 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 5 = 0
5 to 4 = 1
4 to 1 = 3
1 to 5 = 4
Step 3: Combine the filters to a string:
0 1 3 4 = 0134