Step 1: Divide the number into separate digits:
43964 => 4 3 9 6 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
4 to 3 = 1
3 to 9 = 6
9 to 6 = 3
6 to 4 = 2
4 to 4 = 0
Step 3: Combine the filters to a string:
1 6 3 2 0 = 16320