Step 1: Divide the number into separate digits:
42104 => 4 2 1 0 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
4 to 2 => 2
2 to 1 => 1
1 to 0 => 1
0 to 4 => 4
4 to 4 => 0
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
2 => N
1 => C
1 => C
4 => N
0 => E
Step 4: Combine the filters to a string:
N C C N E = NCCNE