Step 1: Divide the number into separate digits:
2388 => 2 3 8 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 3 = 1
3 to 8 = 5
8 to 8 = 0
8 to 2 = 6
Step 3: Combine the filters to a string:
1 5 0 6 = 1506