Step 1: Divide the number into separate digits:
2667 => 2 6 6 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 6 = 4
6 to 6 = 0
6 to 7 = 1
7 to 2 = 5
Step 3: Combine the filters to a string:
4 0 1 5 = 4015