Step 1: Divide the number into separate digits:
2980 => 2 9 8 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 9 = 7
9 to 8 = 1
8 to 0 = 8
0 to 2 = 2
Step 3: Combine the filters to a string:
7 1 8 2 = 7182