Step 1: Divide the number into separate digits:
0861 => 0 8 6 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
0 to 8 = 8
8 to 6 = 2
6 to 1 = 5
1 to 0 = 1
Step 3: Combine the filters to a string:
8 2 5 1 = 8251