## Wednesday, February 19, 2014

### Math archives #5: What's the longest prime number? --with an update

First posted on November 11, 2011.  (11-11-11.  I just thought I'd mention that.)

What would we do without the Internet...

I mentioned recently that a quick check on the current population of Burundi--the subject of a French lesson--showed that there were way more people there than even the (fairly recent) teacher's guide suggested.  That lined up with the fact that we were heading for 7 billion people on Earth by the end of last month.

Today's math history lesson was about the Sieve of Eratosthenes, and the hunt for very large prime numbers.  John Tiner's 2001 book Exploring the World of Mathematics mentioned that the largest discovered to date was over 4 million digits long, which would take about a thousand pages to print out.

On a hunch that that fact too might have been updated, I looked it up.

Yes, the 4-million-digits longest prime was correct in 2001.

But as of 2008, we are up to a number that is 12,978,189 digits long.

And you thought your ID numbers were hard to learn.

2014 Update from Wikipedia:  As of January 2014, the largest known prime number is 257,885,161 − 1, a number with 17,425,170 digits.  (Sourced from this article.)