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 Post subject: Anyone interested in prime numbers?Posted: Wed Jun 01, 2005 8:43 pm

Joined: Sat Apr 16, 2005 4:26 pm
Posts: 5
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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 Post subject: Posted: Tue Nov 15, 2005 8:45 am

Joined: Tue Nov 15, 2005 7:58 am
Posts: 129
Location: Oregon, USA
Um, it wouldn't be prime; by definition, it'd be the product of all the numbers you multiplied together to get it.

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 Post subject: Large prime numbersPosted: Tue Nov 15, 2005 6:12 pm

Joined: Sat Apr 16, 2005 4:26 pm
Posts: 5
Location: Sussex, England
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 numbersPosted: Sat Nov 19, 2005 4:32 am

Joined: Tue Nov 15, 2005 7:58 am
Posts: 129
Location: Oregon, USA
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 numbersPosted: Sun Nov 20, 2005 7:40 pm

Joined: Sat Apr 16, 2005 4:26 pm
Posts: 5
Location: Sussex, England
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 numbersPosted: Mon Nov 21, 2005 1:22 am

Joined: Tue Nov 15, 2005 7:58 am
Posts: 129
Location: Oregon, USA
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 numbersPosted: Tue Nov 22, 2005 6:48 pm

Joined: Sat Apr 16, 2005 4:26 pm
Posts: 5
Location: Sussex, England
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 numbersPosted: Wed Nov 23, 2005 5:15 am

Joined: Tue Nov 15, 2005 7:58 am
Posts: 129
Location: Oregon, USA
oldnovo wrote:
Perhaps you know the problems of going back to poorly documented spaghetti code after a six-month layoff!

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

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 Post subject: Re: Large prime numbersPosted: Wed Nov 23, 2005 11:58 pm

Joined: Mon Dec 27, 2004 11:40 pm
Posts: 318
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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 Post subject: Posted: Thu Nov 24, 2005 12:51 am

Joined: Thu Dec 16, 2004 6:42 pm
Posts: 1115
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

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Prof. Kelly

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 Post subject: Posted: Thu Nov 24, 2005 6:59 am

Joined: Tue Nov 15, 2005 7:58 am
Posts: 129
Location: Oregon, USA
profkelly wrote:
... uncommented 6809 ... converted to 68000 by conversion program.

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

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 Post subject: Posted: Thu Nov 24, 2005 1:16 pm

Joined: Thu Dec 16, 2004 6:42 pm
Posts: 1115

_________________
Prof. Kelly

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