Step 1: Divide the number into separate digits:
36518 => 3 6 5 1 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 6 = 3
6 to 5 = 1
5 to 1 = 4
1 to 8 = 7
8 to 3 = 5
Step 3: Combine the filters to a string:
3 1 4 7 5 = 31475