- --- In primenumbers@yahoogroups.com, "djbroadhurst" <david.broadhurst@...> wrote:
>

I first removed small factors with factorize program from libgmp demos (= trial divisions + Pollard's rho).

>

> Congrats. When I did it, I was running ECM and SNFS in parallel

> and pulled the plug on SNFS when ECM found a p48.

>

> > F(263): one composite factor remaining (in progress).

>

> Here I used GNFS on the C130.

>

> David

>

Then I found all other factors with ECM (using P-1 mode for some of them) except for C118 = 3877828174415305750004694470712933786753853898797149341 * 269073781314228860816753896980501633755080784585248485757620731 for which I directly chose cado-nfs.

For the remaining factor C130 of F(263), I've chosen both ECM and cado-nfs. Still waiting for the result...

cado-nfs is really a cadeau. Thanks to its authors.

JL ---In primenumbers@yahoogroups.com, <thefatphil@...> wrote:

> You only chose that target after

> the arrow had landed, I'm sure.It happened thus:

1) I determined to factorize F(n)=((n^2-9)/4)^2-5 for

n <= 300, completely. As later shown in "factordb", I succeeded.2) Meanwhile I ran OpenPFGW on n in [301,600], hoping for a

quick outlier and found none.3) I estimated the probability of an easily discoverable

completely factorization for n>600 and found it to be small.4) Recalling how I had once been caught out before by

a "probably no more" heuristic, I set a lone process running on

n in [601, 10000] so as not to be caught out again by Jens.5) When I later looked and pfgw.log, it had found a hit at

n=608.So yes, Phil, you are quite correct that the puzzle was set

after this finding. However the heuristic that I gave was

made prior to my discovery, else I would not have said that

I was surprised.The point that you are making (I think) is that I do such

expsriments often and only notice when the result is unexpected.

I don't tell folk about all the boring times when a negative

heuristic is borne out by a null result. That is the selectioneffect.

David

`(guilty of not boring folk with what is routine)`