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-   -   checking big digit number as prime (https://www.mersenneforum.org/showthread.php?t=25538)

drmurat 2020-05-13 08:24

checking big digit number as prime
 
which one is hard . calculating big digit number or checking it . which methods ca be use for checkig numbers ?

[b][color=red][size=4]MODERATOR NOTE:[/size] Thread moved from FermatSearch forum[/color][/b]

Uncwilly 2020-05-13 13:40

Are you asking how hard it is to take 2[SUP]332,199,893[/SUP]-1 and expand it to its full decimal form vs checking it to see if it is prime?
The first is very fast. Faster than the old machines could display it. The second is slow.

If you have some complex formula to calculate the number vs checking it to see if it is prime, even that, calculating the number is faster than checking it (in almost every case).

paulunderwood 2020-05-13 14:29

[QUOTE=Uncwilly;545234]Are you asking how hard it is to take 2[SUP]332,199,893[/SUP]-1 and expand it to its full decimal form vs checking it to see if it is prime?
The first is very fast. Faster than the old machines could display it. The second is slow.

If you have some complex formula to calculate the number vs checking it to see if it is prime, even that, calculating the number is faster than checking it (in almost every case).[/QUOTE]

Just to expand on your "in almost very case". PRP'ing a huge partitions number is quicker than computing its decimal digits (with the latest Pari/GP version). Proving it prime or even checking the certificate is a few orders more time-consuming.

VBCurtis 2020-05-13 17:25

As for "which methods" from the OP question- it depends on the form that describes your number, as well as how big "big digits" is.

Give us more info about what size and what form you have in mind, you'll get a better answer.

drmurat 2020-05-13 17:49

I think I am at the begining . :) I get 2^50.000 at first night with my own code . can we think it is big :) . I am recording all results from 2 ^ 1 to 2 ^ 50000 . and it goes on I want to calculate fermat and mersenne primes

paulunderwood 2020-05-13 18:03

[QUOTE=drmurat;545279]I think I am at the begining . :) I get 2^50.000 at first night with my own code . can we think it is big :) . I am recording all results from 2 ^ 1 to 2 ^ 50000 . and it goes on I want to calculate fermat and mersenne primes[/QUOTE]

If you taking about how long it takes to wrtie the number to file: The following takes ~1 ms with [URL="https://pari.math.u-bordeaux.fr/download.html"]Pari/GP[/URL]:

[CODE]gettime();write("delMe",2^50000+1);gettime()
1
[/CODE]

drmurat 2020-05-13 18:15

I am calculating 2^50000 and writing to file and calcupating 2^50001 and ... goes on . I get 2^60000 . big numbers get years and years ...

Uncwilly 2020-05-13 18:20

Apfloat also works nice: [url]http://www.apfloat.org/apfloat/[/url]
Also [url]http://numcalc.com/[/url] handles it quickly
And 2^50000-1 is not prime. The exponent has to be prime.

drmurat 2020-05-13 18:29

thank you . it will be so helpfull to me . I get 2 ^ 65000

Uncwilly 2020-05-13 18:36

[QUOTE=drmurat;545288]thank you . it will be so helpfull to me . I get 2 ^ 65000[/QUOTE]
What are your plans (please use a paragraph to state it)? If you are just practicing your coding, look at places that can help you learn. If you don't trust what everyone else has done, you have issues. Are you testing the numbers using L-L? Or are you doing it via a more rudimentary way? What language/platform are you using? Why do you want the decimal expansion?

drmurat 2020-05-13 18:48

okay . I am not plannig to improve my coding . I am behind so many thing about primes . I am medical doctor . I know a bit coding . and intrested in with primes nearly 20 mounths .I do my calculations with my own . it has to reason fitst when I need data fot one process . getting whole data is hard . you must open so many zip files . make them as you want . it gets so time . the second reason making calculation with your own gives you a chance of oservation . I am asking here to calculating 2 ^70000 is hard . I realy dont know the answer .


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