Step 1: Divide the number into separate digits:
1541 => 1 5 4 1
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 1 = 3
1 to 1 = 0
Step 3: Combine the filters to a string:
4 1 3 0 = 4130