What do you notice about these arrays? Do any of the arrays have a special or unique shape? What do you notice about the number of arrays that can be made with 16 chairs compared to 17 chairs?
Hopefully, you notice that 16 chairs can be arranged in several different arrays. That is because it has many factors: 1, 2, 4, 8, 16. A number that has more than two factors is called a composite number. You probably noticed that 17 only has two arrays. This is because 17 is a prime number. Any number that has only two factors, one and itself, is a prime number. The factors of 17 are 17 and 1.
Also, you may have noticed that 16 can be arranged into a perfect square with 4 rows and 4 columns. Any number that results when another number is multiplied by itself is a square number. (ex: 3x3=9 Nine is a square number. 5x5=25 Twenty-five is a square number.) Sometimes math vocabulary can be confusing! For a reminder of the meaning of some math words that you may have forgotten, visit this great online math dictionary.
Can you think of any more examples of composite, prime or square numbers? If so, show off what you know by leaving us a comment!