Step 1: Divide the number into separate digits:
3720 => 3 7 2 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 7 = 4
7 to 2 = 5
2 to 0 = 2
0 to 3 = 3
Step 3: Combine the filters to a string:
4 5 2 3 = 4523