Step 1: Divide the number into separate digits:
23617 => 2 3 6 1 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 3 = 1
3 to 6 = 3
6 to 1 = 5
1 to 7 = 6
7 to 2 = 5
Step 3: Combine the filters to a string:
1 3 5 6 5 = 13565