Step 1: Divide the number into separate digits:
65844 => 6 5 8 4 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 5 => 1
5 to 8 => 3
8 to 4 => 4
4 to 4 => 0
4 to 6 => 2
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
1 => C
3 => N
4 => N
0 => E
2 => N
Step 4: Combine the filters to a string:
C N N E N = CNNEN