This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread 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.