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Old 2009-04-30, 20:36   #1
flava
 
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Default Factorial primes search?

In case someone is still keeping track of a factorial prime search, all numbers are tested up to 39200.
I looked up various pages (aparently inactive, got them mostly on archive.org) and picked up the last known status for n!+1 and n!-1 (it was arround n=37000 with some small ranges completed above that number). Normally I'll get to 40000 for both forms in a few months.
If an organized search was still running and someone knows about it, I'd appreciate the info, there is no need to double test right now.

Last fiddled with by flava on 2009-04-30 at 20:52
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Old 2009-04-30, 20:43   #2
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Quote:
Originally Posted by flava View Post
In case someone is still keeping track of a factorial prime search, all numbers are tested up to 39200.
I looked up various pages (aparently inactive, got them mostly on archive.org) and picked up the last known status for n!+1 and n!-1 (it was arround n=37000 with some small ranges, completed above that number). Normally I'll get to 40000 for both forms in a few months.
If an organized search was still running and someone knows about it, I'd appreciate the info, there is no need to double test right now.
Phil Carmody is still coordinating the search, although I don't recall the webpage he uses to do the coordination.
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Old 2009-04-30, 20:48   #3
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perhaps here: http://fatphil.org/maths/factorial/

there's a file with presieved values:
30000<n<100000 and 30011<p<6320124029 from 2002

Last fiddled with by kar_bon on 2009-04-30 at 20:51
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Old 2009-04-30, 20:51   #4
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I am aware of that page but the link to the search is dead and the page seems old (not updated since 2002).
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Old 2009-04-30, 20:54   #5
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here is a german current page: http://www.rechenkraft.net/wiki/inde...itle=Primeform
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Old 2009-04-30, 21:04   #6
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Thanks a lot!
Looks like the range I was working on is already done, except the under 39000 ranges marked "in progress".
I wonder why I didn't find this page. Probably overlooked it, or it wasn't indexed properly at the time I was looking for a factorial prime search.
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Old 2010-11-26, 14:21   #7
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How about k * n! ± 1?

Last fiddled with by 3.14159 on 2010-11-26 at 14:23
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Old 2010-11-26, 15:09   #8
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Quote:
Originally Posted by 3.14159 View Post
How about k * n! ± 1?
I'm not aware of any searches for primes of this form, but I don't off the top of my head if a known primality test can be used on this form.
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Old 2010-11-26, 18:41   #9
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Quote:
Originally Posted by rogue View Post
I'm not aware of any searches for primes of this form, but I don't off the top of my head if a known primality test can be used on this form.
Surely an N-1/N+1 test could be used with any practical k/n picks?

Last fiddled with by Mini-Geek on 2010-11-26 at 18:42
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Old 2010-11-26, 19:30   #10
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Quote:
Originally Posted by rogue View Post
I'm not aware of any searches for primes of this form, but I don't off the top of my head if a known primality test can be used on this form.
http://www.primenumbers.net/Henri/us/FactPrimus.htm
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Old 2010-11-27, 13:49   #11
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Quote:
Originally Posted by rogue View Post
I'm not aware of any searches for primes of this form, but I don't off the top of my head if a known primality test can be used on this form.
Just use an N-1. And primes of this type are very easy to find. And, there might be no sieving necessary for this type.

Ex: 8717*289!+1.

A somewhat larger example; 1085*1950!+1 (5574 digits)

There's also k * p(n)# ± 1, if anyone would like; NewPGen can sieve for this type of prime.

By the way, (I'm unsure if I asked this before), why is it so difficult to sieve for k * n! ± 1 or k * p(n)# ± 1?

Last fiddled with by 3.14159 on 2010-11-27 at 14:12
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