Step 1: Divide the number into separate digits:
85377 => 8 5 3 7 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 5 => 3
5 to 3 => 2
3 to 7 => 4
7 to 7 => 0
7 to 8 => 1
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
3 => N
2 => N
4 => N
0 => E
1 => C
Step 4: Combine the filters to a string:
N N N E C = NNNEC