There are 26 letters in the English alphabet.
How many strings of length n, such that no letter
is repeated twice (or more) in succession, exist?

Examples: for n=4 agir and psop are "permitted", while aggr or ppso are not.

I believe the answer is
26*25^{(n - 1)}

Posted by Dej Mar on 2012-09-24 18:03:51