Step 1: Divide the number into separate digits:
1401 => 1 4 0 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 4 = 3
4 to 0 = 4
0 to 1 = 1
1 to 1 = 0
Step 3: Combine the filters to a string:
3 4 1 0 = 3410