Step 1: Divide the number into separate digits:
9046 => 9 0 4 6
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 0 = 9
0 to 4 = 4
4 to 6 = 2
6 to 9 = 3
Step 3: Combine the filters to a string:
9 4 2 3 = 9423