Step 1: Divide the number into separate digits:
2608 => 2 6 0 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 6 = 4
6 to 0 = 6
0 to 8 = 8
8 to 2 = 6
Step 3: Combine the filters to a string:
4 6 8 6 = 4686