Step 1: Divide the number into separate digits:
30894 => 3 0 8 9 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 0 => 3
0 to 8 => 8
8 to 9 => 1
9 to 4 => 5
4 to 3 => 1
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
3 => N
8 => N
1 => C
5 => N
1 => C
Step 4: Combine the filters to a string:
N N C N C = NNCNC