Step 1: Divide the number into separate digits:
38126 => 3 8 1 2 6
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 8 => 5
8 to 1 => 7
1 to 2 => 1
2 to 6 => 4
6 to 3 => 3
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
5 => N
7 => N
1 => C
4 => N
3 => N
Step 4: Combine the filters to a string:
N N C N N = NNCNN