Step 1: Divide the number into separate digits:
306 => 3 0 6
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 0 => 3
0 to 6 => 6
6 to 3 => 3
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
3 => N
6 => N
3 => N
Step 4: Combine the filters to a string:
N N N = NNN