Step 1: Divide the number into separate digits:
7920 => 7 9 2 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 9 = 2
9 to 2 = 7
2 to 0 = 2
0 to 7 = 7
Step 3: Combine the filters to a string:
2 7 2 7 = 2727