Step 1: Divide the number into separate digits:
9718 => 9 7 1 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 7 = 2
7 to 1 = 6
1 to 8 = 7
8 to 9 = 1
Step 3: Combine the filters to a string:
2 6 7 1 = 2671