Step 1: Divide the number into separate digits:
3498 => 3 4 9 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 4 = 1
4 to 9 = 5
9 to 8 = 1
8 to 3 = 5
Step 3: Combine the filters to a string:
1 5 1 5 = 1515