Step 1: Divide the number into separate digits:
64151 => 6 4 1 5 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 4 = 2
4 to 1 = 3
1 to 5 = 4
5 to 1 = 4
1 to 6 = 5
Step 3: Combine the filters to a string:
2 3 4 4 5 = 23445