Step 1: Divide the number into separate digits:
8251 => 8 2 5 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 2 = 6
2 to 5 = 3
5 to 1 = 4
1 to 8 = 7
Step 3: Combine the filters to a string:
6 3 4 7 = 6347