Step 1: Divide the number into separate digits:
7013 => 7 0 1 3
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 0 => 7
0 to 1 => 1
1 to 3 => 2
3 to 7 => 4
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
7 => N
1 => C
2 => N
4 => N
Step 4: Combine the filters to a string:
N C N N = NCNN