Bill Allombert on Fri, 26 Apr 2013 16:11:39 +0200

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Re: Trying to factor a number a bit but not hanging the program for hours

On Fri, Apr 26, 2013 at 02:57:11PM +0100, Richard in Reading wrote:
> As part of a pari program I'm trying to factor certain large numbers but then give up if a factorization isn't easily achievable. I've been using factorint(n,9) with the expectation that it will always complete reasonably quickly.
> However 
> factorint(19841096725703655581869366691520038810629264428011560812788963464047306742065927607422529,9)
> runs for hours whereas 
> factorint( 450448646198249 * 7187991967803917, 9)
> [3237821250781162225771540741333 1]
> returns straight away even though I'm supplying a composite. 
> Note that factor() returns the above factors in about 0.2 of a second.
> It would be nice to have a decent factoring function which spends a certain
> amount of time trying to factor a number and then gives up. I seem to
> remember seeing a script on the web which could do it in pari using the
> default factoring function but using some function in combination with trap
> to interrupt its execution after a time.
> Can anyone help?