Step 1: Divide the number into separate digits:
7503 => 7 5 0 3
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 3 = 3
3 to 7 = 4
Step 3: Combine the filters to a string:
2 5 3 4 = 2534