Step 1: Divide the number into separate digits:
9185 => 9 1 8 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 1 = 8
1 to 8 = 7
8 to 5 = 3
5 to 9 = 4
Step 3: Combine the filters to a string:
8 7 3 4 = 8734