An analog of the Polyomino composed of Isosceles Right Triangles joined along edges of the same length. The number of polyaboloes composed of triangles are 1, 3, 4, 14, 30, 107, 318, 1106, 3671, ... (Sloane's A006074).
See also Diabolo, Hexabolo, Pentabolo, Tetrabolo, Triabolo
References
Sloane, N. J. A. Sequence
A006074/M2379
in ``An On-Line Version of the Encyclopedia of Integer Sequences.''
http://www.research.att.com/~njas/sequences/eisonline.html and Sloane, N. J. A. and Plouffe, S.
The Encyclopedia of Integer Sequences. San Diego: Academic Press, 1995.