Step 1: Divide the number into separate digits:
9250 => 9 2 5 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 2 => 7
2 to 5 => 3
5 to 0 => 5
0 to 9 => 9
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
7 => N
3 => N
5 => N
9 => C
Step 4: Combine the filters to a string:
N N N C = NNNC