Step 1: Divide the number into separate digits:
8660 => 8 6 6 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 6 = 2
6 to 6 = 0
6 to 0 = 6
0 to 8 = 8
Step 3: Combine the filters to a string:
2 0 6 8 = 2068