When a number
of counters can be displayed in a rectangular pattern with more
than one row or column, then the number concerned is called a rectangle
number. It has at least two factors other than 1, such numbers are
also called composite. They are never prime, but may be square.

A number that can be shown as a pattern of dots which are in the
shape of a rectangle. Such a number must have at least two factors
bigger than one.

Seven is not a rectangular number (factors 1 and
7), whereas ten is (factors 2 and 5).