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Old 2004-05-27, 21:23   #1
clowns789
 
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Jun 2003
The Computer

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Default Faster than LL?

Please tell me if this is pretty obvious.

I noticed that any composite number over 3 could have two primes added up to equal it.

For example:

You want to check if 11 is prime. You go down to the next highest prime, 7. 7+2=9, 7+3=10. Any higher would make what it equals higher. You go down to 5 and find you can't add anything to make it up to 11. Therefore, it is prime.

Tell me how you like it. It seemed pretty simple so I don't think it will actually beat LL.
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Old 2004-05-27, 21:36   #2
Uncwilly
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Aug 2003
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What is the next highest prime to M41?

You have to have knowledge of all primes lower than the number in question, this makes it impractical for titanic numbers, even just hugh numbers.
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Old 2004-05-27, 21:45   #3
cyrix
 
Jul 2003
Thuringia; Germany

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Quote:
Originally Posted by clowns789
Please tell me if this is pretty obvious.

I noticed that any composite number over 3 could have two primes added up to equal it.
Which two primes add to 35? :surprised

Cyrix

Last fiddled with by cyrix on 2004-05-27 at 21:46
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Old 2004-05-27, 23:39   #4
Mike
 
May 2004
Vancouver, Canada

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Quote:
Originally Posted by cyrix
Which two primes add to 35? :surprised

Cyrix
I keep getting 34 But it works if 3 primes are allowed to be added.
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