Step 1: Divide the number into separate digits:
89957 => 8 9 9 5 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 9 => 1
9 to 9 => 0
9 to 5 => 4
5 to 7 => 2
7 to 8 => 1
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
1 => C
0 => E
4 => N
2 => N
1 => C
Step 4: Combine the filters to a string:
C E N N C = CENNC