Step 1: Divide the number into separate digits:
9572 => 9 5 7 2
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 5 = 4
5 to 7 = 2
7 to 2 = 5
2 to 9 = 7
Step 3: Combine the filters to a string:
4 2 5 7 = 4257