Step 1: Divide the number into separate digits:
1256 => 1 2 5 6
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 2 = 1
2 to 5 = 3
5 to 6 = 1
6 to 1 = 5
Step 3: Combine the filters to a string:
1 3 1 5 = 1315