Step 1: Divide the number into separate digits:
13651 => 1 3 6 5 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 3 = 2
3 to 6 = 3
6 to 5 = 1
5 to 1 = 4
1 to 1 = 0
Step 3: Combine the filters to a string:
2 3 1 4 0 = 23140