Step 1: Divide the number into separate digits:
9395 => 9 3 9 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 3 = 6
3 to 9 = 6
9 to 5 = 4
5 to 9 = 4
Step 3: Combine the filters to a string:
6 6 4 4 = 6644