Butterfly Polyiamond

$\begin{figure}\begin{center}\BoxedEPSF{ButterflyTri.epsf scaled 1200}\end{center}\end{figure}$

References

Golomb, S. W. Polyominoes: Puzzles, Patterns, Problems, and Packings, 2nd ed. Princeton, NJ: Princeton University Press, p. 92, 1994.