Step 1: Divide the number into separate digits:
5318 => 5 3 1 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 3 = 2
3 to 1 = 2
1 to 8 = 7
8 to 5 = 3
Step 3: Combine the filters to a string:
2 2 7 3 = 2273