Step 1: Divide the number into separate digits:
68773 => 6 8 7 7 3
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 8 = 2
8 to 7 = 1
7 to 7 = 0
7 to 3 = 4
3 to 6 = 3
Step 3: Combine the filters to a string:
2 1 0 4 3 = 21043