Step 1: Divide the number into separate digits:
18459 => 1 8 4 5 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 8 = 7
8 to 4 = 4
4 to 5 = 1
5 to 9 = 4
9 to 1 = 8
Step 3: Combine the filters to a string:
7 4 1 4 8 = 74148