Step 1: Divide the number into separate digits:
3897 => 3 8 9 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 8 = 5
8 to 9 = 1
9 to 7 = 2
7 to 3 = 4
Step 3: Combine the filters to a string:
5 1 2 4 = 5124