- This is probably THE most embarassing question.... but I am perplexed

to the max.

May I (a novice at this) ask your indulgence for some educating /

verification of a condition?

I have two machines that do most work...

AMD-64 FX series for sieving (16 MP/sec not uncommon).

P4b 2.4G for LLR (ver 3.3 currently).

I have been trying to learn / catch up.

I sieved, for 24 hours as is (I am told) the norm using NPG.

I ran the NPG file and got nothing. Sieved the next block, got

nothing. I went back to the beginning (low N) and started again.

Again... there were no primes found.

After the 4-5th go around, I got deeper into this and went in small

increments...

I did the most rudimentary test: k.b^n-1

using: k=7, b=2, 2<=n<=65536

@ P=1G, K=7,N=29 was in the NPG as the lowest file.

@ P=5G, it was gone... as were MANY of valid K N

(which would yield prime) values.

This has been verified on seperate processors (Intel and AMD).

All machines are Prime95 (Gimps) full torture test certified.

They were also recertified prior to the start of this test run.

Am I using the wrong software; sieving too much; or a known issue?

The Engineer in me says that there smells of a 2^32 wrap around bug @

the P=4G mark w/ or w/o the combo of 2 & 65536 for N.

PS: Since I *SHOULD* know better and be able to solve this myself,

please don't hestitate to slap me around either... LOL :)

I thank you for your time. I thank you in advance for your

assistance.

Chuck > I did the most rudimentary test: k.b^n-1

I am pretty sure that what you are seeing, is that NPG has factored

> using: k=7, b=2, 2<=n<=65536

>

> @ P=1G, K=7,N=29 was in the NPG as the lowest file.

> @ P=5G, it was gone... as were MANY of valid K N

> (which would yield prime) values.

>

the number. The factor found, was the number itself. NPG has made

this choice to NOT check to see if a found factor is "itself", due

to checks like that would slow down the overall speed of NPG, and

it would be assumed that very tiny N such as this would be proven

prime/composite using other trivial methods.

It is simply a run time behavior of NPG which you learn to live with.

If you were concerned about getting those tiny numbers, then I would

recommend using PFGW, and create this file:

ABC2 7*2^$a-1

a: from 1 to 1000

(call the file pfgw.in) Then perform a pfgw -f pfgw.in. There will

be 2 files, a pfgw-prime.log (proven primes proven by trial division)

and a file pfgw.log with the PRP-3's. Then simply run

pfgw -tp pfgw.log and all the primes will be in pfgw-prime.log.

Then use NPG from n=1000 up to whatever limit you want.

Or you could simply look on the web page:

http://www.prothsearch.net/riesel2.html

and find all known 7*2^n-1 up to n=1100000

Jim.- Chuck wrote:

> I sieved, for 24 hours as is (I am told) the norm using NPG.

The norm for any sieve is to sieve until the removal rate is similar to the

prp/test time (which may be a complicated issue for a fixed k sieve).

> I did the most rudimentary test: k.b^n-1

The prime 7*2^29-1 = 3758096383 is between 1G and 5G (G = 10^9).

> using: k=7, b=2, 2<=n<=65536

>

> @ P=1G, K=7,N=29 was in the NPG as the lowest file.

> @ P=5G, it was gone... as were MANY of valid K N

> (which would yield prime) values.

As Jim also thinks, NewPGen probably removed it when the prime was found as

factor of itself.

Some of my sieves knowingly do the same.

Users and programmers can argue about whether something is a bug or feature.

If NewPGen also removes some known primes above the sieve limit:

Can you give examples?

Have you checked "Verify results" ?

The help says:

If "Verify results" is checked, NewPGen will do a careful check to make sure

that the prime actually does divide the number that it thinks it does. This

will make NewPGen very slightly slower, but it is recommended that it is

always checked, particularly as p gets large (where the scope for programming

errors increases)

If you check "Log the numbers removed" in the Options menu then NewPGen will

write which prime removes a candidate, but only for primes above 2^32.

--

Jens Kruse Andersen > I did the most rudimentary test: k.b^n-1

As other have stated, those numbers are being removed because the numbers

> using: k=7, b=2, 2<=n<=65536

>

> @ P=1G, K=7,N=29 was in the NPG as the lowest file.

> @ P=5G, it was gone... as were MANY of valid K N

> (which would yield prime) values.

themselves are being found as factors. I could change the software to catch

that; thinking about it it might be fairly easy to perform one additional

check while removing from the bitmap.

Regards,

Paul.

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