Step 1: Divide the number into separate digits:
6820 => 6 8 2 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 8 = 2
8 to 2 = 6
2 to 0 = 2
0 to 6 = 6
Step 3: Combine the filters to a string:
2 6 2 6 = 2626