Step 1: Divide the number into separate digits:
19781 => 1 9 7 8 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 9 = 8
9 to 7 = 2
7 to 8 = 1
8 to 1 = 7
1 to 1 = 0
Step 3: Combine the filters to a string:
8 2 1 7 0 = 82170