A little known fact about prime numbers

Posted by E-George on November 20, 2007

Did you know that 1 is not a prime number? Well it’s not. No, really. It’s not. Lookit:

In mathematics, a prime number (or a prime) is a natural number which has exactly two distinct natural number divisors: 1 and itself. An infinitude of prime numbers exists, as demonstrated by Euclid in about 300 BC. The first thirty prime numbers are:

2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113

Why should you care about this? You should care because some day you may be asked to create a prime number calculator that is required to display all prime numbers between 0 and some input, x. If your prime number calculator spits out 0,1,2,3,5… and so on, than it’s wrong. It should spit out 2,3,5,7… and so on. I was listening to a classmate flippantly describe prime numbers as any number that is divisible by 1 and itself. While true, they missed that bit about the divisors have to be distinct (or unique), thereby ruling out 0 and 1. Simple logic and a little recollection of fourth-grade division tables should recall that you can’t divide zero by any number as it creates an indeterminate case, and because of the nature of 1, there are no two distinct numbers that can divide into it. Therefore, 1 is not a prime number - it is merely an odd number.

I give this to you as a way to break the ice at the series of holiday parties that should be kicking off in the next couple of weeks.

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