Step 1: Divide the number into separate digits:
5913 => 5 9 1 3
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 9 = 4
9 to 1 = 8
1 to 3 = 2
3 to 5 = 2
Step 3: Combine the filters to a string:
4 8 2 2 = 4822