The largest known Prime number was discovered in August 2008.
It has about 12.9 million digits - so we won't be reproducing it here!
It is one less than 2 raised to the 43112609th power:
243112609_-1"Other primes have been found since then but they are smaller numbers.
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257,885,161 -1 as of 2013. New primes are being calculated all the time, so this will change as new and larger ones are discovered. Also, note that there are infinitely many primes (proved by Euclid around 300 BCE), so there won't ever be a single "highest" prime, only the highest one known.
September has 19 days that are prime numbers Note: 1 is not prime or composite
September has thirty days. Of the numbers 1-30, the following are prime: 2,3,5,7,11,13,17,19,23,29. The others are composite, except 1 which is neither! So, 10 primes, 19 composites, and 1
Average
Think of the numbers on the number line as years, months, or dates of the month. You could explain the event in a text box close to the corresponding date, then draw an arrow from the box to the location of the date on the number line.