Step 1: Divide the number into separate digits:
6049 => 6 0 4 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 0 = 6
0 to 4 = 4
4 to 9 = 5
9 to 6 = 3
Step 3: Combine the filters to a string:
6 4 5 3 = 6453