Step 1: Divide the number into separate digits:
7505 => 7 5 0 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 5 = 2
5 to 0 = 5
0 to 5 = 5
5 to 7 = 2
Step 3: Combine the filters to a string:
2 5 5 2 = 2552