Step 1: Divide the number into separate digits:
68707 => 6 8 7 0 7
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 0 = 7
0 to 7 = 7
7 to 6 = 1
Step 3: Combine the filters to a string:
2 1 7 7 1 = 21771