Step 1: Divide the number into separate digits:
31192 => 3 1 1 9 2
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 1 = 2
1 to 1 = 0
1 to 9 = 8
9 to 2 = 7
2 to 3 = 1
Step 3: Combine the filters to a string:
2 0 8 7 1 = 20871