Step 1: Divide the number into separate digits:
0791 => 0 7 9 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
0 to 7 = 7
7 to 9 = 2
9 to 1 = 8
1 to 0 = 1
Step 3: Combine the filters to a string:
7 2 8 1 = 7281