Step 1: Divide the number into separate digits:
3753 => 3 7 5 3
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 7 = 4
7 to 5 = 2
5 to 3 = 2
3 to 3 = 0
Step 3: Combine the filters to a string:
4 2 2 0 = 4220