Step 1: Divide the number into separate digits:
80423 => 8 0 4 2 3
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 0 = 8
0 to 4 = 4
4 to 2 = 2
2 to 3 = 1
3 to 8 = 5
Step 3: Combine the filters to a string:
8 4 2 1 5 = 84215