Step 1: Divide the number into separate digits:
7768 => 7 7 6 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 7 = 0
7 to 6 = 1
6 to 8 = 2
8 to 7 = 1
Step 3: Combine the filters to a string:
0 1 2 1 = 0121