Step 1: Divide the number into separate digits:
9568 => 9 5 6 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 5 = 4
5 to 6 = 1
6 to 8 = 2
8 to 9 = 1
Step 3: Combine the filters to a string:
4 1 2 1 = 4121