Step 1: Divide the number into separate digits:
32815 => 3 2 8 1 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 2 => 1
2 to 8 => 6
8 to 1 => 7
1 to 5 => 4
5 to 3 => 2
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
1 => C
6 => N
7 => N
4 => N
2 => N
Step 4: Combine the filters to a string:
C N N N N = CNNNN