Step 1: Divide the number into separate digits:
3738 => 3 7 3 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 7 = 4
7 to 3 = 4
3 to 8 = 5
8 to 3 = 5
Step 3: Combine the filters to a string:
4 4 5 5 = 4455