Step 1: Divide the number into separate digits:
6864 => 6 8 6 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 8 = 2
8 to 6 = 2
6 to 4 = 2
4 to 6 = 2
Step 3: Combine the filters to a string:
2 2 2 2 = 2222