Step 1: Divide the number into separate digits:
12405 => 1 2 4 0 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 2 = 1
2 to 4 = 2
4 to 0 = 4
0 to 5 = 5
5 to 1 = 4
Step 3: Combine the filters to a string:
1 2 4 5 4 = 12454