Step 1: Divide the number into separate digits:
6658 => 6 6 5 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 6 = 0
6 to 5 = 1
5 to 8 = 3
8 to 6 = 2
Step 3: Combine the filters to a string:
0 1 3 2 = 0132