Date: Dec 6, 2012 7:33 PM Author: Jonathan J. Crabtree Subject: Ways kids can make and build prime numbers. Re: A Good Activity Re: http://mathforum.org/kb/thread.jspa?threadID=2419007

Hi Bob,

Your son may be too old for Santa, yet he may like to share the following with littlies who are yet to believe in numbers.

Santa says every child at kindergarten gets a toy set this Christmas, and the toys are counting numbers less than 100!

So how will the elves most efficiently create all the sets of numbers?

Simple! They will test out the toys to see if they can multi-play them to make the next number one more than the previous.

They will start at the toy set with a unit, also called 1, and ask, "Can I multiplay this 1 to make 2?

No! So 2 will be INCLUDED in the set and the set will contain 1, 2.

Can we multiplay the toys to make the next number one more than two, which is three?

No! So 3 will be INCLUDED in the toy set.

1, 2, 3.

Can we multiplay the toys to make a 4?

Yes! So the number 4 will be omitted from the toy set. (The elves are pushing to a deadline!)

Can we multiplay the toys to make a 5?

No! So 5 will be INCLUDED in the set.

1, 2, 3, 5.

Can we multiplay the toys to make a 6? Yes, so it will be omitted as kids can multiplay 3 x 2 and 2 x 3.

Can we multiplay the toys to make a 7? No, so it is INCLUDED in the set.

1, 2, 3, 5, 7.

Can we multiplay the toys to make an 8? Yes, omit it as 2 x 2 x 2 is 8. (Remember we won't have a 4 in the toy set).

Can we multiplay the toys to make a 9? Yes, omit it as 3 x 3 is 9.

Can we multiplay the toys to make a 10? Yes, omit it as 5 x 2 is 10.

Can we multiplay the toys to make an 11? No, so INCLUDE it in the set.

1, 2, 3, 5, 7, 9, 11...

And so up and on the elves went, so every child at kinder could play with his or her elementary prime numbers later at school. The toys were much loved!

By associating with various elves, pretty soon Santa became an expert at commuting to and fro and distributing all the toys, yet that is another story.

So that is why after the bonus 1 unit is unwrapped, the other toys in the set are:

2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, and 97.

Another way to build a set of primes is to make four sided shapes on the floor from a set of 100 toy cubic blocks.

Every time you can't make a rectangle with a bunch of blocks, that number of blocks will be one of your child's prime numbers!

Jonathan Crabtree

P.S. To argue about the merits of 1 as a prime is not the point of this post. The point is numbers can be fun this Christmas and provide a lifetime of enjoyment.

P.P.S Happy Christmas, Season's Greetings and Happy Holidays to all who read this.