Step 1: Divide the number into separate digits:
8174 => 8 1 7 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 1 = 7
1 to 7 = 6
7 to 4 = 3
4 to 8 = 4
Step 3: Combine the filters to a string:
7 6 3 4 = 7634