Step 1: Divide the number into separate digits:
7136 => 7 1 3 6
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 1 = 6
1 to 3 = 2
3 to 6 = 3
6 to 7 = 1
Step 3: Combine the filters to a string:
6 2 3 1 = 6231