Step 1: Divide the number into separate digits:
2415 => 2 4 1 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 4 = 2
4 to 1 = 3
1 to 5 = 4
5 to 2 = 3
Step 3: Combine the filters to a string:
2 3 4 3 = 2343