Step 1: Divide the number into separate digits:
74347 => 7 4 3 4 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 4 => 3
4 to 3 => 1
3 to 4 => 1
4 to 7 => 3
7 to 7 => 0
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
3 => N
1 => C
1 => C
3 => N
0 => E
Step 4: Combine the filters to a string:
N C C N E = NCCNE