Step 1: Divide the number into separate digits:
67197 => 6 7 1 9 7
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 9 = 8
9 to 7 = 2
7 to 6 = 1
Step 3: Combine the filters to a string:
1 6 8 2 1 = 16821