Step 1: Divide the number into separate digits:
0151 => 0 1 5 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
0 to 1 = 1
1 to 5 = 4
5 to 1 = 4
1 to 0 = 1
Step 3: Combine the filters to a string:
1 4 4 1 = 1441