Prime Numbers

Mersenne PrimeA prime number is a number that is divisible only by one and by itself. Factors are numbers that can be divided into a number with no remainder. The factors of 18 are the numbers 1, 2, 3, 6, 9, and 18, The number 18 is divisible by each of these factors. We call that a composite number. But the number 19 has only two factors, 1 and 19. Thus, the number 19 is a prime number. In order, the first few prime numbers are 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53... 1 isn't a prime number because it only has one factor, itself.

The ancient Greeks were the first to speculate on prime numbers, and Euclid was the first to come up with a mathematical proof that prime numbers continue infinitely. There is no known formula for determining prime numbers. To find one, you have to see if a specific number is divisible by any lower number. With very large numbers, that's not easy to determine. But with the advent of the computer, scientists and mathematicians continue to push the boundary of defining the largest prime number. Currently, the top known prime number is (2 raised to the power of 13466917) -1. Without the microprocessor doing all the heavy lifting, it is doubtful we would have come close to such a large number. But despite all this focus on prime numbers, no pattern has yet emerged allowing for a formula for determining further prime numbers.

About the Author

Gene Mascoli, JD

Gene MascoliGene Mascoli is a founder and publisher of He holds a J.D. degree from the University of Santa Clara and a B.A. in English. In 1997 Gene launched, an online science education portal where he brought together his love of writing with his interest in the sciences. Gene collaborated with David Gamon on the popular digital book “The Internet Guide to NASA on the Net” and has also produced two popular science CD-ROMs on astronomy and space science.