Step 1: Divide the number into separate digits:
97989 => 9 7 9 8 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 7 => 2
7 to 9 => 2
9 to 8 => 1
8 to 9 => 1
9 to 9 => 0
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
2 => N
2 => N
1 => C
1 => C
0 => E
Step 4: Combine the filters to a string:
N N C C E = NNCCE