Step 1: Divide the number into separate digits:
3589 => 3 5 8 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 5 = 2
5 to 8 = 3
8 to 9 = 1
9 to 3 = 6
Step 3: Combine the filters to a string:
2 3 1 6 = 2316