Step 1: Divide the number into separate digits:
1534 => 1 5 3 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 5 = 4
5 to 3 = 2
3 to 4 = 1
4 to 1 = 3
Step 3: Combine the filters to a string:
4 2 1 3 = 4213