Step 1: Divide the number into separate digits:
16161 => 1 6 1 6 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 6 = 5
6 to 1 = 5
1 to 6 = 5
6 to 1 = 5
1 to 1 = 0
Step 3: Combine the filters to a string:
5 5 5 5 0 = 55550