Step 1: Divide the number into separate digits:
8751 => 8 7 5 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 7 = 1
7 to 5 = 2
5 to 1 = 4
1 to 8 = 7
Step 3: Combine the filters to a string:
1 2 4 7 = 1247