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Old 2007-01-19, 19:06   #12
michaf
 
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small succes:

91268055041 | 22^134217728+1

So at least THAT one isn't prime :)
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Old 2007-01-20, 00:43   #13
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Quote:
Originally Posted by michaf View Post
small succes:

91268055041 | 22^134217728+1

So at least THAT one isn't prime :)
That's about one millionth of a second's work. Why is it considered a success?
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Old 2007-01-20, 03:23   #14
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Originally Posted by fatphil View Post
That's about one millionth of a second's work. Why is it considered a success?
He's probably thinking of how long it would take to test the number for primality if it hadn't been sieved.
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Old 2007-01-20, 08:03   #15
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Quote:
Originally Posted by jasong View Post
He's probably thinking of how long it would take to test the number for primality if it hadn't been sieved.
That was indeed what I was thinking :)
_and_ it took some 24 hours to get to that sieving point :>
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Old 2007-01-20, 08:20   #16
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Quote:
Originally Posted by michaf View Post
That was indeed what I was thinking :)
_and_ it took some 24 hours to get to that sieving point :>
Should have taken you less than a sec!

Anyway why are you trying to factorize these numbers
For base 22, numbers that are multiple of 22 do not have to be tested, this eliminates k=22,484 but k=1 is left. But 1*22^1+1 is prime hence 1 is eliminated.

under base=100 only the following bases are left for which k does not produce a prime
38
50
62
68
86
92
98
You can try to find a prime for them

Last fiddled with by Citrix on 2007-01-20 at 08:45
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Old 2007-01-20, 18:29   #17
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Quote:
Originally Posted by michaf View Post
Without any math skills... so excuse me if I bugger here :>

base 22:

22*22^n + 1
=
22^(n+1) + 1
=
1*22^(n+1) + 1

so, k = 1
and that one is eliminated, therefore is k=22 and 484?
Quote:
Unfortunately not. 1*22^1+1=23 prime, but, I think we decided for the Sierpinski base 5 exercise, that we would not use n=0, otherwise k=22 could be eliminated but not 484.
(quotes from sierpinski 6-18 thread)
I think this justifies the search
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Old 2007-01-20, 23:24   #18
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Quote:
Originally Posted by Citrix View Post
Should have taken you less than a sec!
Oh, how do you do that? Test for all factors upto that limit in a sec? :)
Or did you mean just testing if that one number divided the huge number?
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Old 2007-01-21, 02:34   #19
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Quote:
Originally Posted by michaf View Post
Oh, how do you do that? Test for all factors upto that limit in a sec? :)
Or did you mean just testing if that one number divided the huge number?
Finding the factor should take less than 1 sec. Try to factor 1 number at a time. What numbers are left, I can try to prove them composite them for you.
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Old 2007-01-21, 09:58   #20
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Hmm... what am I doing wrong then?

srsieve is sieving about 20-30Million p's per second, but not a huge amount more when sieving only 1 n.
Or is srsieve the wrong program here?
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Old 2007-01-21, 11:11   #21
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Quote:
Originally Posted by michaf View Post
Hmm... what am I doing wrong then?

srsieve is sieving about 20-30Million p's per second, but not a huge amount more when sieving only 1 n.
Or is srsieve the wrong program here?
Try PFGW.
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Old 2007-01-21, 12:54   #22
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Quote:
Originally Posted by Citrix View Post
Try PFGW.
I couldn't notice anything quicker about pfgw's factoring routines then there is in srsieve (quite the opposite, actually).

What's pfgw's command to find "91268055041 | 22^134217728+1" quickly?
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