Step 1: Divide the number into separate digits:
1844 => 1 8 4 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 8 = 7
8 to 4 = 4
4 to 4 = 0
4 to 1 = 3
Step 3: Combine the filters to a string:
7 4 0 3 = 7403