Knuth's <i>Art of Computer Programming, vol 2</i> [1], not surprisingly, gives a thorough discussion of the balanced ternary system.<p>The solution for a nice brainteaser can be found quickly once one thinks about balanced trinary, here it is: "Using a balance scale, what is the minimum number of wheights needed to weigh any whole number of grams up to 40g?"<p>[1] <a href="http://www.amazon.com/Art-Computer-Programming-Volume-Seminumerical/dp/0201896842" rel="nofollow">http://www.amazon.com/Art-Computer-Programming-Volume-Seminu...</a>