Step 1: Divide the number into separate digits:
8437 => 8 4 3 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 4 = 4
4 to 3 = 1
3 to 7 = 4
7 to 8 = 1
Step 3: Combine the filters to a string:
4 1 4 1 = 4141