Question 27
To enter Burian's castle, one must use a password of at least 6 characters. No character may occur twice or more consecutively, and no consecutive pair of characters may occur elsewhere in the password. Only the keys $E,N,V$ still work. How many different passwords can be tried?
(A) 6 (B) 18 (C) $6^2$ (D) $2^6$ (E) infinitely many.
(A) 6 (B) 18 (C) $6^2$ (D) $2^6$ (E) infinitely many.