Step 1: Divide the number into separate digits:
9844 => 9 8 4 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 8 = 1
8 to 4 = 4
4 to 4 = 0
4 to 9 = 5
Step 3: Combine the filters to a string:
1 4 0 5 = 1405