Step 1: Divide the number into separate digits:
5165 => 5 1 6 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 1 = 4
1 to 6 = 5
6 to 5 = 1
5 to 5 = 0
Step 3: Combine the filters to a string:
4 5 1 0 = 4510