Step 1: Divide the number into separate digits:
18043 => 1 8 0 4 3
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 8 = 7
8 to 0 = 8
0 to 4 = 4
4 to 3 = 1
3 to 1 = 2
Step 3: Combine the filters to a string:
7 8 4 1 2 = 78412