Step 1: Divide the number into separate digits:
64189 => 6 4 1 8 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 4 => 2
4 to 1 => 3
1 to 8 => 7
8 to 9 => 1
9 to 6 => 3
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
2 => N
3 => N
7 => N
1 => C
3 => N
Step 4: Combine the filters to a string:
N N N C N = NNNCN