Step 1: Divide the number into separate digits:
18919 => 1 8 9 1 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 8 = 7
8 to 9 = 1
9 to 1 = 8
1 to 9 = 8
9 to 1 = 8
Step 3: Combine the filters to a string:
7 1 8 8 8 = 71888