Step 1: Divide the number into separate digits:
7867 => 7 8 6 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 8 = 1
8 to 6 = 2
6 to 7 = 1
7 to 7 = 0
Step 3: Combine the filters to a string:
1 2 1 0 = 1210