Step 1: Divide the number into separate digits:
856 => 8 5 6
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 5 => 3
5 to 6 => 1
6 to 8 => 2
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
3 => N
1 => C
2 => N
Step 4: Combine the filters to a string:
N C N = NCN