Step 1: Divide the number into separate digits:
1766 => 1 7 6 6
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 7 = 6
7 to 6 = 1
6 to 6 = 0
6 to 1 = 5
Step 3: Combine the filters to a string:
6 1 0 5 = 6105