Step 1: Divide the number into separate digits:
90089 => 9 0 0 8 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 0 = 9
0 to 0 = 0
0 to 8 = 8
8 to 9 = 1
9 to 9 = 0
Step 3: Combine the filters to a string:
9 0 8 1 0 = 90810