Step 1: Divide the number into separate digits:
1544 => 1 5 4 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 5 = 4
5 to 4 = 1
4 to 4 = 0
4 to 1 = 3
Step 3: Combine the filters to a string:
4 1 0 3 = 4103