Step 1: Divide the number into separate digits:
57844 => 5 7 8 4 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 7 => 2
7 to 8 => 1
8 to 4 => 4
4 to 4 => 0
4 to 5 => 1
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
2 => N
1 => C
4 => N
0 => E
1 => C
Step 4: Combine the filters to a string:
N C N E C = NCNEC