Step 1: Divide the number into separate digits:
13800 => 1 3 8 0 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 3 = 2
3 to 8 = 5
8 to 0 = 8
0 to 0 = 0
0 to 1 = 1
Step 3: Combine the filters to a string:
2 5 8 0 1 = 25801