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PostPosted: Wed Jun 01, 2005 8:43 pm 
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Location: Sussex, England
With the prospect of getting rich quick, I naively thought if I could sieve the first 16 million integers for primes and multiply them together I might end up with a 10 million digit prime number. Well, I got my million-plus prime numbers with Easy68k and after 3 days had multiplied together primes up to around 330,000 - then reality set in! Even if after a few months, or longer, I got a 10 million digit number, how do I set about trying to prove primality? Its been an interesting exercise and after last programming the 6809 some 20 years ago, its has been fun to get to grips with the 68000 via EASy68K.


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PostPosted: Tue Nov 15, 2005 8:45 am 
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Um, it wouldn't be prime; by definition, it'd be the product of all the numbers you multiplied together to get it. :cry:


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 Post subject: Large prime numbers
PostPosted: Tue Nov 15, 2005 6:12 pm 
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Indeed it could not be prime, but adding one to the total would give a number that I believe could possibly be prime, but is very much more likely to factorise and that all one can say is that there will not be a factor less than the last prime in the sequence of the product of successive primes.


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 Post subject: Re: Large prime numbers
PostPosted: Sat Nov 19, 2005 4:32 am 
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oldnovo wrote:
Indeed it could not be prime, but adding one to the total would give a number that I believe could possibly be prime, but is very much more likely to factorise and that all one can say is that there will not be a factor less than the last prime in the sequence of the product of successive primes.


Have you generated and tested the first few dozen such numbers (product of primes + 1)?

I tried it with 32-bit math, but of course didn't get very far. :)


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 Post subject: Large prime numbers
PostPosted: Sun Nov 20, 2005 7:40 pm 
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Yes, I generated the prime products+1 up to the limit of 32 bit math to prove my 68k BCD math multiplication routine worked, but it was not until I tested primality of these numbers with an old version (3) of Mathematica that I realised I was unlikely to be successful in my search for very large prime numbers.


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 Post subject: Re: Large prime numbers
PostPosted: Mon Nov 21, 2005 1:22 am 
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oldnovo wrote:
... my 68k BCD math multiplication routine ...

I'd like to see that! Would you mind posting it?


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 Post subject: Re: Large prime numbers
PostPosted: Tue Nov 22, 2005 6:48 pm 
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I'll see if I can get something together. Perhaps you know the problems of going back to poorly documented spaghetti code after a six-month layoff!


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 Post subject: Re: Large prime numbers
PostPosted: Wed Nov 23, 2005 5:15 am 
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oldnovo wrote:
Perhaps you know the problems of going back to poorly documented spaghetti code after a six-month layoff!

Only too well :roll:
... but of course, that wasn't 68000 code! Poor 68000 code??? Is that possible? :)


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 Post subject: Re: Large prime numbers
PostPosted: Wed Nov 23, 2005 11:58 pm 
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gtippery wrote:
Poor 68000 code??? Is that possible? :)

Oh indeedy! Just go browse through the code in any Amiga PD collection, especially the demos. Just don't do it with any sharp implements nearby. 8^)=

Lee.


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PostPosted: Thu Nov 24, 2005 12:51 am 
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Oh baby, do I have some horror stories to tell.

Try working on 68000 code, originally written in uncommented 6809 by someone who no longer works for the company and then converted to 68000 by conversion program. :? Ouch! Makes my head hurt just thinking about it and that was 15 years ago :lol:

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Prof. Kelly


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PostPosted: Thu Nov 24, 2005 6:59 am 
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profkelly wrote:
... uncommented 6809 ... converted to 68000 by conversion program.:lol:

I believe the technical term for the result of this process is "coprolite". :lol:


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PostPosted: Thu Nov 24, 2005 1:16 pm 
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:lol:

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