A warehouse system creates a 3-character aisle code c_1 c_2 c_3 from the symbol set A, B, C, D, E, F, G, H, which contains 2 vowels A, E and 6 consonants. The code requires that characters in odd positions (c_1 and c_3) must be vowels, and adjacent characters cannot match (c_2 ≠ c_1 and c_3 ≠ c_2).