Step 1: Divide the number into separate digits:
97090 => 9 7 0 9 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 7 = 2
7 to 0 = 7
0 to 9 = 9
9 to 0 = 9
0 to 9 = 9
Step 3: Combine the filters to a string:
2 7 9 9 9 = 27999