Step 1: Divide the number into separate digits:
71123 => 7 1 1 2 3
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 1 => 6
1 to 1 => 0
1 to 2 => 1
2 to 3 => 1
3 to 7 => 4
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
6 => N
0 => E
1 => C
1 => C
4 => N
Step 4: Combine the filters to a string:
N E C C N = NECCN