Step 1: Divide the number into separate digits:
9216 => 9 2 1 6
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 2 = 7
2 to 1 = 1
1 to 6 = 5
6 to 9 = 3
Step 3: Combine the filters to a string:
7 1 5 3 = 7153