Step 1: Divide the number into separate digits:
2677 => 2 6 7 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 6 = 4
6 to 7 = 1
7 to 7 = 0
7 to 2 = 5
Step 3: Combine the filters to a string:
4 1 0 5 = 4105