Step 1: Divide the number into separate digits:
9649 => 9 6 4 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 6 => 3
6 to 4 => 2
4 to 9 => 5
9 to 9 => 0
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
3 => N
2 => N
5 => N
0 => E
Step 4: Combine the filters to a string:
N N N E = NNNE