Step 1: Divide the number into separate digits:
31445 => 3 1 4 4 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 1 => 2
1 to 4 => 3
4 to 4 => 0
4 to 5 => 1
5 to 3 => 2
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
2 => N
3 => N
0 => E
1 => C
2 => N
Step 4: Combine the filters to a string:
N N E C N = NNECN