Step 1: Divide the number into separate digits:
0169 => 0 1 6 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
0 to 1 = 1
1 to 6 = 5
6 to 9 = 3
9 to 0 = 9
Step 3: Combine the filters to a string:
1 5 3 9 = 1539