Step 1: Divide the number into separate digits:
63942 => 6 3 9 4 2
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 3 => 3
3 to 9 => 6
9 to 4 => 5
4 to 2 => 2
2 to 6 => 4
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
3 => N
6 => N
5 => N
2 => N
4 => N
Step 4: Combine the filters to a string:
N N N N N = NNNNN