Step 1: Divide the number into separate digits:
7573 => 7 5 7 3
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 5 = 2
5 to 7 = 2
7 to 3 = 4
3 to 7 = 4
Step 3: Combine the filters to a string:
2 2 4 4 = 2244