Step 1: Divide the number into separate digits:
3192 => 3 1 9 2
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 1 => 2
1 to 9 => 8
9 to 2 => 7
2 to 3 => 1
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
2 => N
8 => N
7 => N
1 => C
Step 4: Combine the filters to a string:
N N N C = NNNC