Step 1: Divide the number into separate digits:
1580 => 1 5 8 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 5 = 4
5 to 8 = 3
8 to 0 = 8
0 to 1 = 1
Step 3: Combine the filters to a string:
4 3 8 1 = 4381