Step 1: Divide the number into separate digits:
65099 => 6 5 0 9 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 5 = 1
5 to 0 = 5
0 to 9 = 9
9 to 9 = 0
9 to 6 = 3
Step 3: Combine the filters to a string:
1 5 9 0 3 = 15903