Step 1: Divide the number into separate digits:
02990 => 0 2 9 9 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
0 to 2 = 2
2 to 9 = 7
9 to 9 = 0
9 to 0 = 9
0 to 0 = 0
Step 3: Combine the filters to a string:
2 7 0 9 0 = 27090