Step 1: Divide the number into separate digits:
90619 => 9 0 6 1 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 0 => 9
0 to 6 => 6
6 to 1 => 5
1 to 9 => 8
9 to 9 => 0
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
9 => C
6 => N
5 => N
8 => N
0 => E
Step 4: Combine the filters to a string:
C N N N E = CNNNE