Step 1: Divide the number into separate digits:
77724 => 7 7 7 2 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 7 => 0
7 to 7 => 0
7 to 2 => 5
2 to 4 => 2
4 to 7 => 3
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
0 => E
0 => E
5 => N
2 => N
3 => N
Step 4: Combine the filters to a string:
E E N N N = EENNN