Step 1: Divide the number into separate digits:
80918 => 8 0 9 1 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 0 = 8
0 to 9 = 9
9 to 1 = 8
1 to 8 = 7
8 to 8 = 0
Step 3: Combine the filters to a string:
8 9 8 7 0 = 89870