Step 1: Divide the number into separate digits:
0406 => 0 4 0 6
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
0 to 4 = 4
4 to 0 = 4
0 to 6 = 6
6 to 0 = 6
Step 3: Combine the filters to a string:
4 4 6 6 = 4466