Step 1: Divide the number into separate digits:
7184 => 7 1 8 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 1 = 6
1 to 8 = 7
8 to 4 = 4
4 to 7 = 3
Step 3: Combine the filters to a string:
6 7 4 3 = 6743