Step 1: Divide the number into separate digits:
57099 => 5 7 0 9 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 7 = 2
7 to 0 = 7
0 to 9 = 9
9 to 9 = 0
9 to 5 = 4
Step 3: Combine the filters to a string:
2 7 9 0 4 = 27904