Step 1: Divide the number into separate digits:
64735 => 6 4 7 3 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 4 => 2
4 to 7 => 3
7 to 3 => 4
3 to 5 => 2
5 to 6 => 1
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
2 => N
3 => N
4 => N
2 => N
1 => C
Step 4: Combine the filters to a string:
N N N N C = NNNNC