Step 1: Divide the number into separate digits:
7865 => 7 8 6 5
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 5 = 1
5 to 7 = 2
Step 3: Combine the filters to a string:
1 2 1 2 = 1212