Step 1: Divide the number into separate digits:
51573 => 5 1 5 7 3
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 1 = 4
1 to 5 = 4
5 to 7 = 2
7 to 3 = 4
3 to 5 = 2
Step 3: Combine the filters to a string:
4 4 2 4 2 = 44242