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Old 2010-11-27, 16:10   #12
CRGreathouse
 
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And, there might be no sieving necessary for this type.
I certainly sieved when I last had a project relating to primes of this form. Why wouldn't a person?
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Old 2010-11-27, 17:29   #13
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I certainly sieved when I last had a project relating to primes of this form. Why wouldn't a person?
I was thinking along the lines of the larger factorials, which are already divisible by most of the small primes. (Ex: k * 4000! + 1.)

Besides, this type of prime is too easy to find, and sieving doesn't get rid of much.

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Old 2010-11-27, 17:35   #14
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I was thinking along the lines of the larger factorials, which are already divisible by most of the small primes. (Ex: k * 4000! + 1.).
But larger factorials also takes more time to test, so you'll have to sieve _more_, not less.
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Old 2010-11-27, 19:18   #15
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But larger factorials also takes more time to test, so you'll have to sieve _more_, not less.
There won't be much eliminated as you head towards the larger factorials. No difference is made.

Last fiddled with by 3.14159 on 2010-11-27 at 19:21
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Old 2010-11-27, 23:45   #16
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There won't be much eliminated as you head towards the larger factorials. No difference is made.
Ok.
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Old 2010-11-28, 04:24   #17
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I was thinking along the lines of the larger factorials, which are already divisible by most of the small primes. (Ex: k * 4000! + 1.)
Yes, I started my sieving above the factorial argument of course.

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Besides, this type of prime is too easy to find, and sieving doesn't get rid of much.
I trust you know the rule of thumb here. It still applies, and suggests that some amount of trial division is still worthwhile. The amount depends on how many you're sieving out and how fast your basic operations are.
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Old 2010-12-04, 01:46   #18
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Yes, I started my sieving above the factorial argument of course.



I trust you know the rule of thumb here. It still applies, and suggests that some amount of trial division is still worthwhile. The amount depends on how many you're sieving out and how fast your basic operations are.
For sieving to be worthwhile in terms of the larger factorials, you'd need a pretty large range; A range of about 10^8 or so.

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Old 2010-12-04, 05:24   #19
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For sieving to be worthwhile in terms of the larger factorials, you'd need a pretty large range; A range of about 10^8 or so.
Only if you have a very slow siever (or quite small factorials).
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