Triplicate Pentominoes
Each
pentomino
shape may be built from 9 smaller pentominoes. Often, this is
done by eliminating (from the set of 12 pentominoes) the shape that is to be
built along with 2 other pentominoes.
An example of a triplicate X pentomino is shown below.
See also
Pentomino Puzzles,
The Centroid of a Pentomino