Step 1: Divide the number into separate digits:
8405 => 8 4 0 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 4 = 4
4 to 0 = 4
0 to 5 = 5
5 to 8 = 3
Step 3: Combine the filters to a string:
4 4 5 3 = 4453