Composite being Prime

kruoli · 2018-02-15, 18:28

Hey,

why is FactorDB refusing a primality certificate on 23801#+1 and why does it think that this number is composite? I found others examples in the past but could not find them again in the moment. :|
Looking at MathWorld, it is already a proven prime, so I have no doubts in this (especially after I did a certificate with primo).

Greetings,
Oliver!

paulunderwood · 2018-02-15, 19:04

It is a known issue of FactorDB's handling of "#".

axn · 2018-02-16, 02:48

Quote:

Originally Posted by paulunderwood

It is a known issue of FactorDB's handling of "#".

I'm aware of the issue of handling ## (because PFGW doesn't know ##). Didn't know that there was one for #?!

paulunderwood · 2018-02-16, 09:00

Quote:

Originally Posted by axn

I'm aware of the issue of handling ## (because PFGW doesn't know ##). Didn't know that there was one for #?!

You are probably right, but if you click on "number" field on http://factordb.com/index.php?query=23801%23%2B1 you get 1+2647##

axn · 2018-02-16, 09:40

Quote:

Originally Posted by paulunderwood

You are probably right, but if you click on "number" field on http://factordb.com/index.php?query=23801%23%2B1 you get 1+2647##

Aha! So factordb understands that number with ## representation, and PFGW checked 2647#+1, which is a composite. Mystery solved.

Syd needs to find all numbers with an internal ## representation and fix it. Probably not gonna happen anytime soon.

EdH · 2018-02-16, 16:54

Quote:

Originally Posted by axn

Aha! So factordb understands that number with ## representation, and PFGW checked 2647#+1, which is a composite. Mystery solved.

Syd needs to find all numbers with an internal ## representation and fix it. Probably not gonna happen anytime soon.

I'm up to four known ## candidate PRPs below 4xxx dd. I have my scripts skip them.

2018-02-15, 18:28	#1
kruoli "Oliver" Sep 2017 Porta Westfalica, DE 7²·11 Posts	Composite being Prime Hey, why is FactorDB refusing a primality certificate on 23801#+1 and why does it think that this number is composite? I found others examples in the past but could not find them again in the moment. :\| Looking at MathWorld, it is already a proven prime, so I have no doubts in this (especially after I did a certificate with primo). Greetings, Oliver!

2018-02-15, 19:04	#2
paulunderwood Sep 2002 Database er0rr 3,739 Posts	It is a known issue of FactorDB's handling of "#". Last fiddled with by paulunderwood on 2018-02-15 at 19:14

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