Step 1: Divide the number into separate digits:
2657 => 2 6 5 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 6 = 4
6 to 5 = 1
5 to 7 = 2
7 to 2 = 5
Step 3: Combine the filters to a string:
4 1 2 5 = 4125