Step 1: Divide the number into separate digits:
4028 => 4 0 2 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
4 to 0 = 4
0 to 2 = 2
2 to 8 = 6
8 to 4 = 4
Step 3: Combine the filters to a string:
4 2 6 4 = 4264