Step 1: Divide the number into separate digits:
3767 => 3 7 6 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 7 => 4
7 to 6 => 1
6 to 7 => 1
7 to 3 => 4
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
4 => N
1 => C
1 => C
4 => N
Step 4: Combine the filters to a string:
N C C N = NCCN