Step 1: Divide the number into separate digits:
9007 => 9 0 0 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 0 => 9
0 to 0 => 0
0 to 7 => 7
7 to 9 => 2
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
9 => C
0 => E
7 => N
2 => N
Step 4: Combine the filters to a string:
C E N N = CENN