Feeling in your prime? Obviously the researchers at Central Missouri State University are. They have identified the largest known prime number. In case you don’t know, a prime number is a number that can only be divided by itself and one – like 1, 2, 3, 5, 7, 11, 13, 17, 19, 23, etc. This number is 9.1 million digits long. The number is 2 to the 30,402,457th power minus 1.

Okay, so why all the hoopla? What possible uses are there for prime numbers anyway? To find out the answer I went to my best source for finding out useless stuff, John. Here are four of his reasons for why it is good to find new prime numbers:

1. They are cool and interesting. (a very nerdy answer)
2. They are used in encryption. (an actual useful reason)
3. They gave Eratosthenes a reason for inventing the Sieve of Eratosthenes. (wha?)
4. They keep math professors employed. (what I figured)

Not familiar with the Sieve of Eratosthenes? Since I had to go through the humiliation of not knowing either, here it is.

Imagine a giant (actually infinitely big) piece of paper. On this paper is a grid of all numbers. Circle the number 1 and then starting with 2, circle it, and then cross out all the multiples of 2. Go to the next number that is not crossed out, 3. Circle it. Then cross out all the multiples of 3. Go to the next number that is not crossed out, 5. (You crossed out 4 when you were getting rid of multiples of 2.) Circle 5 and then cross out all of the multiples of 5. (Some numbers will be crossed out multiple times.) Then the next uncrossed out number, 7, and cross out its multiples. And so on. Now when you have gone as far as you’d like to go, take a hole punch and punch out all the numbers that are circled. They are the prime numbers and what you’ve got left is what looked like a sieve to Eratosthenes.

It’s so fun being married to John.

P.S. After I wrote and published this I had the opportunity to have explained to me “more than I wanted to know.” This is a familiar event in our house when you ask John a question. Sarah and Jon were often the recipients of this when they asked for some simple explanation on a homework problem. Anyway, I am now the possessor of great prime number knowledge. I know all about encryption and also why you can prove that there can always be another larger prime number. sigh

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