Step 1: Divide the number into separate digits:
9531 => 9 5 3 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 5 = 4
5 to 3 = 2
3 to 1 = 2
1 to 9 = 8
Step 3: Combine the filters to a string:
4 2 2 8 = 4228