Step 1: Divide the number into separate digits:
6108 => 6 1 0 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 1 = 5
1 to 0 = 1
0 to 8 = 8
8 to 6 = 2
Step 3: Combine the filters to a string:
5 1 8 2 = 5182