Step 1: Divide the number into separate digits:
56996 => 5 6 9 9 6
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 6 => 1
6 to 9 => 3
9 to 9 => 0
9 to 6 => 3
6 to 5 => 1
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
1 => C
3 => N
0 => E
3 => N
1 => C
Step 4: Combine the filters to a string:
C N E N C = CNENC