Step 1: Divide the number into separate digits:
15939 => 1 5 9 3 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 5 = 4
5 to 9 = 4
9 to 3 = 6
3 to 9 = 6
9 to 1 = 8
Step 3: Combine the filters to a string:
4 4 6 6 8 = 44668