Step 1: Divide the number into separate digits:
67181 => 6 7 1 8 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 7 = 1
7 to 1 = 6
1 to 8 = 7
8 to 1 = 7
1 to 6 = 5
Step 3: Combine the filters to a string:
1 6 7 7 5 = 16775