I inaccurately wrote: << 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).

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Correction: I read Thane's question too fast. The statement above addresses only the question of whether a triangle with n dots on a side can be tiled by copies of the 3-dot triangle (2 dots on a side). On the other hand, copies of the 3-dot straight line can never tile a dotty triangle. --Dan ________________________________________________________________________________________ "Outside of a dog, a book is man's best friend. Inside of a dog, it's too dark to read." --Groucho Marx