Step 1: Divide the number into separate digits:
2554 => 2 5 5 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 5 = 3
5 to 5 = 0
5 to 4 = 1
4 to 2 = 2
Step 3: Combine the filters to a string:
3 0 1 2 = 3012