## 18 May 2009

### Primality of 1

When I was in school, I remember them teaching that a prime number was any number divisible by only 1 and itself. Thus, in school, they taught that 1 was prime. Since then, I have noticed that everyone insists that 1 is not prime. Since many of the patterns I find work better with 1 being prime, I decided to try to figure out why the discrepancy...

From Wikipedia:

Until the 19th century, most mathematicians considered the number 1 a prime, with the definition being just that a prime is divisible only by 1 and itself but not requiring a specific number of distinct divisors. There is still a large body of mathematical work that is valid despite labelling 1 a prime, such as the work of Stern and Zeisel. Derrick Norman Lehmer's list of primes up to 10,006,721, reprinted as late as 1956,[2] started with 1 as its first prime.[3] Henri Lebesgue is said to be the last professional mathematician to call 1 prime.[citation needed] The change in label occurred so that the fundamental theorem of arithmetic, as stated, is valid, i.e., “each number has a unique factorization into primes.”[4][5]
So there you have it. They decided in the last 43 years that 1 could no longer be prime so that one of their theorems could be correct. Why does that remind me of someone fudging statistics?

I know, I know... soapbox, right? First the divide-by-zero post, then this... How about this, as soon as we can explain all our math in simple fractals without saying things like "except 0 or 1" or "with n>1", then I'll change my position on it.

Thus Theorem 1 of Hardy & Wright (1979) takes the form, “Every positive integer, except 1, is a product of primes”
bah humbug ;)