Step 1: Divide the number into separate digits:
9691 => 9 6 9 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 6 = 3
6 to 9 = 3
9 to 1 = 8
1 to 9 = 8
Step 3: Combine the filters to a string:
3 3 8 8 = 3388