See this web page: < http://faculty.plattsburgh.edu/don.west/tiling/ >. The short version: It can be done if and only if n == 0, 2, 9, or 11 (mod 12). --Dan --------------- Thane wrote: << I found a short note from Martin Gardner to David A Klarner in my garage (long story; anyway...) The letter is dated 4 Oct 1983. This is what it says (in part) * * * *begin quotation * * * Do you know whether an n-rowed triangle-shaped array of dots like this * * * * * * * * * * ..... can be tiled by single triangles shaped like this * * * or by 1x3 straight lines like this * * * It's been driving me nuts for two weeks! Is there a coloring argument? Martin ******* end quotation *****

...

________________________________________________________________________________________ "Outside of a dog, a book is man's best friend. Inside of a dog, it's too dark to read." --Groucho Marx