This week's book giveaways are in the Refactoring and Agile forums. We're giving away four copies each of Re-engineering Legacy Software and Docker in Action and have the authors on-line! See this thread and this one for details.
One thing though - the number of combinations grows exponentially as you add more (unique) letters. For example, 6 unique characters already gives you 6! = 720 options, and by adding one different letter you already have 7 times as much: 5040.