Step 1: Divide the number into separate digits:
3816 => 3 8 1 6
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 8 = 5
8 to 1 = 7
1 to 6 = 5
6 to 3 = 3
Step 3: Combine the filters to a string:
5 7 5 3 = 5753