Step 1: Divide the number into separate digits:
61871 => 6 1 8 7 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 1 = 5
1 to 8 = 7
8 to 7 = 1
7 to 1 = 6
1 to 6 = 5
Step 3: Combine the filters to a string:
5 7 1 6 5 = 57165