Step 1: Divide the number into separate digits:
73208 => 7 3 2 0 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 3 => 4
3 to 2 => 1
2 to 0 => 2
0 to 8 => 8
8 to 7 => 1
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
4 => N
1 => C
2 => N
8 => N
1 => C
Step 4: Combine the filters to a string:
N C N N C = NCNNC