Step 1: Divide the number into separate digits:
9024 => 9 0 2 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 0 = 9
0 to 2 = 2
2 to 4 = 2
4 to 9 = 5
Step 3: Combine the filters to a string:
9 2 2 5 = 9225