Quote:
Originally Posted by gd_barnes
Please change srsieve to remove the error check for divisibility by 2 and then force the regular sieve process to remove the terms divisible by 2 instead. Is that really difficult? It seems like a simple fix. I'm pretty sure I or others have requested this before and we seem to keep getting the runaround about it.
To be more specific below is what Sweety and I and others want to do when attempting to test a conjecture such as (13*43^n1)/2 if the form is not found to have a smallish prime using simple trial factoring with PFGW.
1. Sieve using srsieve using the form 13*43^n1 but with a starting sieve depth of 3 using the following command:
srsieve G p 3 P 1e9 n 25e3 N 100e3 m 1e9 "13*43^n1"
This tells srsieve to only sieve the form for P=3 to 1e9. That way it does not remove the terms that are divisible by 2 (which would be all of them in this case).
2. Test with PFGW using a standard PFGW header of:
(ABC $a*43^$b1)/2 // {number_primes,$a,1}
13 25007
13 25019
(etc.)
This allows us to both sieve and test the form (13*43^n1)/2. Srsieve currently works for us if we have a form with a prime divisor other than 2 such as (13*46^n1)/3. In that case we would just have it sieve the range of P=5 to 1e9 and there would be no error as there is in the case of (13*43^n1)/2.
Does this make sense?
[ All of these are examples. They are not actual work done.]
If this cannot be done please let us know and we will not request it anymore. We would prefer not to have to run a separate program when standard srsieve will work for 99% of cases like this. Also please let us know how you would sieve the form (13*43^n1)/2. That would be very helpful.

The divisor of k*b^n+1 (+ for Sierp,  for Riesel) is always gcd(k+1,b1) (+ for Sierp,  for Riesel) (see post
https://mersenneforum.org/showpost.p...&postcount=230), since gcd(k+1,b1) is the trivial factor of k*b^n+1, it is simply to take out this factor, thus, the divisor of R43, k=13 is 6, not 2 (gcd(131,431) = 6), and the formula of R43, k=13 is (13*43^n1)/6, not (13*43^n1)/2