Step 1: Divide the number into separate digits:
43911 => 4 3 9 1 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
4 to 3 => 1
3 to 9 => 6
9 to 1 => 8
1 to 1 => 0
1 to 4 => 3
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
1 => C
6 => N
8 => N
0 => E
3 => N
Step 4: Combine the filters to a string:
C N N E N = CNNEN