Step 1: Divide the number into separate digits:
6044 => 6 0 4 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 0 = 6
0 to 4 = 4
4 to 4 = 0
4 to 6 = 2
Step 3: Combine the filters to a string:
6 4 0 2 = 6402