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Is 1 Prime, and Does It Matter?

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11–20 of 162 posts

Re: Is 1 Prime, and Does It Matter?

#12

If 1 is prime, then the fundamental theorem of arithmetic goes from "every positive integer can be written as a product* of primes in one and only one way" to "every positive integer can be written as a product of primes greater than 1 in one and only one way". Doesn't quite have the same ring to it. So just from an aesthetic perspective, no I'd rather 1 isn't a prime number. * empty products being 1 of course

Isn't "every positive integer can be written as a product of primes greater than 1 in one and only one way" incorrect? A prime number is a only product of itself * 1, isn't it?

1 is not greater than 1, and a product of one prime is still a product of primes

Re: Is 1 Prime, and Does It Matter?

#13

I think we’ll need to wait for an answer to if there is a prime number generating function. At that time we can determine if 1 is prime. If it’s found that Eratosthenes’ sieve is the only prime generating function then we have our answer.

We'd have our answer in what way?

Re: Is 1 Prime, and Does It Matter?

#15

If 1 is prime, then the fundamental theorem of arithmetic goes from "every positive integer can be written as a product* of primes in one and only one way" to "every positive integer can be written as a product of primes greater than 1 in one and only one way". Doesn't quite have the same ring to it. So just from an aesthetic perspective, no I'd rather 1 isn't a prime number. * empty products being 1 of course

Isn't "every positive integer can be written as a product of primes greater than 1 in one and only one way" incorrect? A prime number is a only product of itself * 1, isn't it?

Mathematicians generally feel that a single number qualifies as a "product of 1 number." So 7 can be written as just 7 which is still considered a product of prime(s). This is purely a convention thing to make it so theorems can be stated more succinctly, as with not counting 1 as prime.

Re: Is 1 Prime, and Does It Matter?

#16

If 1 is prime, then the fundamental theorem of arithmetic goes from "every positive integer can be written as a product* of primes in one and only one way" to "every positive integer can be written as a product of primes greater than 1 in one and only one way". Doesn't quite have the same ring to it. So just from an aesthetic perspective, no I'd rather 1 isn't a prime number. * empty products being 1 of course

i remember something from math class about "1" and "prime" being special cases of "units" and "irreducible" (?) that made me think these kinds of definitions are much more complicated than we want them to be regardless.

The first part of your comment is completely correct. The latter is a matter of taste, of course. I think the main thing that can be said for a lot of the definitions we have in algebra is that the ones we're using are the ones that stood the test of time because they turned out to be useful. The distinction between invertible elements (units) and irreducible elements, while complicated, also gave us a conceptual framework allowing us to prove lots of interesting and useful theorems.

Re: Is 1 Prime, and Does It Matter?

#18
Other good nerd-sniping math questions:

0^0 = 1? Yes, it’s simpler that way.

0! = 1? Yes, it’s simpler that way.

0/0 = ∞? No, it’s undefined.

0.9999… = 1? Yes, it’s just two ways of expressing the same number.

1+2+3+… = -1/12? No, but if it did have a finite value, that’s what it would be.

Re: Is 1 Prime, and Does It Matter?

#19

I think we’ll need to wait for an answer to if there is a prime number generating function. At that time we can determine if 1 is prime. If it’s found that Eratosthenes’ sieve is the only prime generating function then we have our answer.

We'd have our answer in what way?

I apologize for the ambiguity, it’s apparent when you’ve read the article as it addresses this specific point.

Namely, if the sieve is the only generating function for all of the primes then 1 would need to be omitted as prime as removing its factors would remove every number, thus failing to generate the list of primes.

Re: Is 1 Prime, and Does It Matter?

#20
post #3

One reason that 1 is often excluded from the prime numbers is that if it was included, it would complicate the theorems, proofs, and exposition by the endless repetition of "not equal to 1".

> One reason that 1 is often excluded from the prime numbers is that if it was included, it would complicate the theorems, proofs, and exposition by the endless repetition of "not equal to 1".

This is true and compelling as things developed, but I think it's an explanation of where history brought us, rather than a logical inevitability. For example, I can easily imagine, in a different universe, teachers patiently explaining that we declare that the empty set is not a set, to avoid complicating theorems, proofs, and exposition by the endless repetition of "non-empty set."

(I agree that this is different, because there's no interesting "unique factorization theorem" for sets, but I can still imagine things developing this way. And, indeed, there are complications caused by allowing the empty set in a model of a structure, and someone determined to do so can make themselves pointlessly unpopular by asking "but have you considered the empty manifold?" and similar questions. See also https://mathoverflow.net/questions/45951/interesting-example....)

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