Step 1: Divide the number into separate digits:
9239 => 9 2 3 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 2 = 7
2 to 3 = 1
3 to 9 = 6
9 to 9 = 0
Step 3: Combine the filters to a string:
7 1 6 0 = 7160