Step 1: Divide the number into separate digits:
12839 => 1 2 8 3 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 2 = 1
2 to 8 = 6
8 to 3 = 5
3 to 9 = 6
9 to 1 = 8
Step 3: Combine the filters to a string:
1 6 5 6 8 = 16568