[seqfan] Re: Integers k of the form (2^m + 1) / (2^n + 1)

[Tomasz Ordowski]

Neil, well what can I say?

Max, thanks for resurrecting my sequence!

Best,

Tom Ordo

niedz., 18 lut 2024 o 17:09 Max Alekseyev <maxale at gmail.com> napisał(a):

> It is now https://oeis.org/A370425
>
> Regards,
> Max
>
>
> On Sun, Feb 18, 2024 at 11:01 AM Neil Sloane <njasloane at gmail.com> wrote:
>
> > Too late, I already recycled A370377.  The A-number will have been reused
> > by now.  Can you reconstruct it with a new A-number, and tell me what it
> > is.  Then I will modify the Wiki page of Deleted Sequences to indicate
> that
> > it has been renumbered, not recycled.
> >
> > Best regards
> > Neil
> >
> > Neil J. A. Sloane, Chairman, OEIS Foundation.
> > Also Visiting Scientist, Math. Dept., Rutgers University,
> > Email: njasloane at gmail.com
> >
> >
> >
> > On Sun, Feb 18, 2024 at 10:50 AM Max Alekseyev <maxale at gmail.com> wrote:
> >
> > > Oh, I see the issue now - https://oeis.org/A079665 is sorted as an
> > > irregular triangular array.
> > > Row s contains numbers corresponding to suitable r (co-divisors to odd
> > > divisors of s).
> > > Number 1 may or may not be included in each row (we can leave it out to
> > > keep it more consistent with the current data).
> > > I will clarify the definition of A079665.
> > >
> > > And I take back my suggestion to discard A370377 - sorry for confusion.
> > >
> > > Regards,
> > > Max
> > >
> > >
> > > On Sun, Feb 18, 2024 at 10:33 AM Neil Sloane <njasloane at gmail.com>
> > wrote:
> > >
> > > > I followed Max's suggestion
> > > > Best regards
> > > > Neil
> > > >
> > > > Neil J. A. Sloane, Chairman, OEIS Foundation.
> > > > Also Visiting Scientist, Math. Dept., Rutgers University,
> > > > Email: njasloane at gmail.com
> > > >
> > > >
> > > >
> > > > On Sun, Feb 18, 2024 at 10:23 AM Max Alekseyev <maxale at gmail.com>
> > wrote:
> > > >
> > > > > Sequence of such numbers is already present as
> > > https://oeis.org/A079665
> > > > > which however rather artificially excludes number 1.
> > > > > I'd suggest relaxing the definition of https://oeis.org/A079665 to
> > > > include
> > > > > 1, and discard the draft of A370377.
> > > > >
> > > > > Regards,
> > > > > Max
> > > > >
> > > > > On Sat, Feb 17, 2024 at 2:09 AM Tomasz Ordowski <
> > > > tomaszordowski at gmail.com>
> > > > > wrote:
> > > > >
> > > > > > Dear Sequence Fans!
> > > > > >
> > > > > > The numbers k > 0 for which the equation
> > > > > > 2^m + k = k*2^n + 1 has a solution m,n > 0
> > > > > > are integers of the form (2^m - 1) / (2^n - 1),
> > > > > > i.e. if an only if n divides m. I wrote about it.
> > > > > > See https://oeis.org/A064896 (my comment).
> > > > > > Primes of the sequence A064896 are A245730.
> > > > > > See https://oeis.org/A245730 (all these primes).
> > > > > > Contains: all Mersenne primes, all Fermat primes,
> > > > > > and other primes {73, 262657, 4432676798593, ...}.
> > > > > >    Contrary to appearances, a sufficiently large number k of this
> > > form
> > > > > > cannot be a dual Sierpinski number, but may be a dual Riesel
> > number.
> > > > > >
> > > > > > The numbers k for which the equation
> > > > > > 2^m - k = k*2^n - 1 has a solution m,n > 0
> > > > > > are integers of the form (2^m + 1) / (2^n + 1).
> > > > > > Note that if 2^n+1 divides 2^m+1, then n divides m.
> > > > > > 1, 3, 11, 13, 43, 57, 171, 205, 241, 683, 993, 2731, 3277, ...
> > > > > > This important sequence is not found on the OEIS websites.*
> > > > > > Something related. See A281728 for primes in this sequence:
> > > > > > https://oeis.org/A281728 (unfortunately, without definition
> > there).
> > > > > > Question: are these exactly primes of the form (2^m+1)/(2^n+1)?
> > > > > >     Appearances are deceiving again,
> > > > > > because a sufficiently large number k of this form
> > > > > > cannot be a dual Riesel number, but may be a dual Sierpinski
> > number.
> > > > > >
> > > > > > Best,
> > > > > >
> > > > > > Tom Ordo
> > > > > > _________________
> > > > > > (*) See my new draft: https://oeis.org/draft/A370377
> > > > > > https://oeis.org/A076336 (Sierpinski numbers).
> > > > > > https://oeis.org/A101036 (Riesel numbers).
> > > > > >
> > > > > > --
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