Step 1: Divide the number into separate digits:
1788 => 1 7 8 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 7 = 6
7 to 8 = 1
8 to 8 = 0
8 to 1 = 7
Step 3: Combine the filters to a string:
6 1 0 7 = 6107