Step 1: Divide the number into separate digits:
7418 => 7 4 1 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 4 = 3
4 to 1 = 3
1 to 8 = 7
8 to 7 = 1
Step 3: Combine the filters to a string:
3 3 7 1 = 3371