Step 1: Divide the number into separate digits:
3925 => 3 9 2 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 9 = 6
9 to 2 = 7
2 to 5 = 3
5 to 3 = 2
Step 3: Combine the filters to a string:
6 7 3 2 = 6732