Step 1: Divide the number into separate digits:
66191 => 6 6 1 9 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 6 = 0
6 to 1 = 5
1 to 9 = 8
9 to 1 = 8
1 to 6 = 5
Step 3: Combine the filters to a string:
0 5 8 8 5 = 05885