Step 1: Divide the number into separate digits:
1592 => 1 5 9 2
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 5 = 4
5 to 9 = 4
9 to 2 = 7
2 to 1 = 1
Step 3: Combine the filters to a string:
4 4 7 1 = 4471