Time again for our Website of the Week, when we showcase interesting and innovative online destinations.

This week, it's a website that takes us to a seemingly simple but sophisticated and elegant corner of the world of mathematics.

CALDWELL: "The Prime Pages are a collection of pages about prime numbers. The most important feature of the Prime Pages is the database of the largest known primes. I also have pages that discuss the mathematics behind finding the primes and who's doing the primes."

Chris Caldwell is the prime guy behind the Prime Pages at prime.utm.edu. He's a math professor at the University of Tennessee at Martin, whose interest in primes hints at their fascinating story.

CALDWELL: "I got interested in primes because it's such a simple idea, but the mathematics behind it is really surprisingly complicated."

Prime numbers, as you may remember from school, can be evenly divided by only themselves and one. So five and seven are primes, but not six, which can be divided by two and three.

Modern math theory and fast computers have advanced the study of prime numbers, but it's a tradition that goes back more than 2,000 years.

CALDWELL: "The ancient Babylonians about 300 BC did have multiplication tables and tables showing division into primes. As a study, as an organized study of mathematics, prime numbers begin with Euclid, who discussed them in his geometry book, *The Elements*."

Prime numbers have a fascination for mathematicians, but there are some real-world uses for primes.

CALDWELL: "For example, one use of prime numbers is for cryptology. It turns out that you can multiply two big primes together and use that as the basis of a secret code."

When Prof. Caldwell talks about big prime numbers, we're talking REALLY big. The largest prime number verified to date, in the database on the Prime Pages website, is two to the 30,402,457th power minus one — a number with more than nine million digits. And there are still bigger ones yet to be found, since — as Euclid proved — there are an infinite number of prime numbers.

The Prime Pages are online at primes.utm.edu, or get the link from our site, VOANews.com.