Step 1: Divide the number into separate digits:
84018 => 8 4 0 1 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 4 => 4
4 to 0 => 4
0 to 1 => 1
1 to 8 => 7
8 to 8 => 0
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
4 => N
4 => N
1 => C
7 => N
0 => E
Step 4: Combine the filters to a string:
N N C N E = NNCNE