The twelve 5-Polyominoes illustrated above and known by the letters of the alphabet they most closely resemble: (Gardner 1960).
References
Ball, W. W. R. and Coxeter, H. S. M. Mathematical Recreations and Essays, 13th ed. New York:
Dover, pp. 110-111, 1987.
Dudeney, H. E. ``The Broken Chessboard.'' Problem 74 in The Canterbury Puzzles and Other Curious Problems, 7th ed.
London: Thomas Nelson and Sons, pp. 119-120, 1949.
Gardner, M. ``Mathematical Games: More About the Shapes that Can Be Made with Complex Dominoes.'' Sci. Amer. 203,
186-198, Nov. 1960.
Hunter, J. A. H. and Madachy, J. S. Mathematical Diversions. New York: Dover, pp. 80-86, 1975.
Lei, A. ``Pentominoes.'' http://www.cs.ust.hk/~philipl/omino/pento.html.
Ruskey, F. ``Information on Pentomino Puzzles.''
http://sue.csc.uvic.ca/~cos/inf/misc/PentInfo.html.