Step 1: Divide the number into separate digits:
2425 => 2 4 2 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 4 = 2
4 to 2 = 2
2 to 5 = 3
5 to 2 = 3
Step 3: Combine the filters to a string:
2 2 3 3 = 2233