Step 1: Divide the number into separate digits:
32688 => 3 2 6 8 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 2 => 1
2 to 6 => 4
6 to 8 => 2
8 to 8 => 0
8 to 3 => 5
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
1 => C
4 => N
2 => N
0 => E
5 => N
Step 4: Combine the filters to a string:
C N N E N = CNNEN