Date: Dec 6, 2012 2:16 PM
Author: Paul A. Tanner III
Subject: Re: A Good Activity
On Thu, Dec 6, 2012 at 11:06 AM, Robert Hansen <bob@rsccore.com> wrote:

> The other night, my son and I worked out all the primes less than 100.

>

One of the "little theorems" or "tricks" on the primes that could come in handy is that all primes greater than 3 are either 1 less or 1 greater than some multiple of 6 - the set of all primes greater than 3 is a subset of of the set of all positive integers 6c-1 or 6c+1 for all positive integers c. (It makes it easier to recall all the primes up to whatever number - just count up multiples of six and at each count try to recall which of the two numbers in question are composite and which of the two are prime.

I wrote two messages using this fact with respect to primes at sci.math about a decade ago, to share some things I found with respect to the Twin Prime Conjecture:

"Twin prime conjecture restated without reference to primes"

http://mathforum.org/kb/message.jspa?messageID=507327

"Re: Twin prime conjecture restated without reference to primes"

http://mathforum.org/kb/message.jspa?messageID=507328