Step 1: Divide the number into separate digits:
1304 => 1 3 0 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 3 => 2
3 to 0 => 3
0 to 4 => 4
4 to 1 => 3
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
2 => N
3 => N
4 => N
3 => N
Step 4: Combine the filters to a string:
N N N N = NNNN