[seqfan] Re: -5 is not a prime

[Robert Gerbicz]

"This is wrong, and dangerous (it has led people to make mistakes in
sequences).
If negative numbers were primes we would lose unique factorization, a
cornerstone of mathematics."

No, you're wrong, check out
https://en.wikipedia.org/wiki/Unique_factorization_domain
, say 5 and -5 are associated so the factorization of 15=3*5=(-5)*(-3) up
to ordering and association is the same.
And https://en.wikipedia.org/wiki/Prime_element .

Neil Sloane <njasloane at gmail.com> ezt írta (időpont: 2021. jan. 3., V,
18:02):

> Amiram Eldar tells me that Mathematica considers -1 times a prime to be a
> prime.
>
> Select[Range[-10, 10], PrimeQ]
> {-7, -5, -3, -2, 2, 3, 5, 7}
>
> This is wrong, and dangerous (it has led people to make mistakes in
> sequences).
>
> If negative numbers were primes we would lose unique factorization, a
> cornerstone of mathematics.
>
> --
> Seqfan Mailing list - http://list.seqfan.eu/
>