Step 1: Divide the number into separate digits:
42891 => 4 2 8 9 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
4 to 2 = 2
2 to 8 = 6
8 to 9 = 1
9 to 1 = 8
1 to 4 = 3
Step 3: Combine the filters to a string:
2 6 1 8 3 = 26183