Step 1: Divide the number into separate digits:
4654 => 4 6 5 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
4 to 6 = 2
6 to 5 = 1
5 to 4 = 1
4 to 4 = 0
Step 3: Combine the filters to a string:
2 1 1 0 = 2110