[seqfan] Re: A089755

Neil Sloane njasloane at gmail.com
Sun Sep 20 13:16:44 CEST 2015


Allan, You are right! The binary version of A262356 would begin
1,2,3,4,5,6,8,7,12,9,10,11,13,20,...
Can you please submit it?
An important sequence not in the OEIS.
Clearly a permutation of the natural numbers.

Best regards
Neil

Neil J. A. Sloane, President, OEIS Foundation.
11 South Adelaide Avenue, Highland Park, NJ 08904, USA.
Also Visiting Scientist, Math. Dept., Rutgers University, Piscataway, NJ.
Phone: 732 828 6098; home page: http://NeilSloane.com
Email: njasloane at gmail.com


On Sat, Sep 19, 2015 at 6:17 PM, Allan Wechsler <acwacw at gmail.com> wrote:

> If I understood Reinhard's variant properly, then the binary variant should
> start 1,2,3,4,5,6,8,7,12, and this isn't in OEIS either.
>
>
> On Sat, Sep 19, 2015 at 4:15 PM, M. F. Hasler <oeis at hasler.fr> wrote:
>
> > PS: IMHO it was not absolutely required to add a(1)=11 in the definition
> > (of course it does not harm to "spell this out", though)
> > because one can consider that this is implied by
> > "single digit primes are not allowed unless they arise from [a(n-1)
> > having 0 as 2nd digit]":
> > a(1) = 11 is the smallest prime compatible with this definition,
> > because for the first term a(n-1) is empty => has no 0 as 2nd digit =>
> > a single digit prime is not allowed.
> > --
> > Maximilian
> >
> > On Sat, Sep 19, 2015 at 4:00 PM, M. F. Hasler <oeis at hasler.fr> wrote:
> > > David, did you have a look at the version
> > > https://oeis.org/history/view?seq=A089755&v=38
> > > I proposed since yesterday, a few hours before your message to seqfan ?
> > >
> > > On Sat, Sep 19, 2015 at 9:43 AM, David Wilson <
> davidwwilson at comcast.net>
> > wrote:
> > >> Regarding A089755:
> > >>
> > >> I was finally able to cob together a program that almost works.
> > >>
> > >> Let "new" mean "not occurring previously in the sequence".
> > >>
> > >> Given element n, I cobbed together the following rule for computing
> the
> > next element n':
> > >>
> > >> if (n is a single-digit number)
> > >> {
> > >>         n' = smallest new prime starting with n;
> > >> }
> > >> else if (next to last digit of n is 0)
> > >> {
> > >>         Remove leading digit of n;
> > >>         n' = smallest new prime starting with n;
> > >> }
> > >> else
> > >> {
> > >>         Remove leading digit of n;
> > >>         n' = smallest new prime > n starting with n;
> > >> }
> > >>
> > >> This rule is rather obscure and complicated, and is not deducible from
> > the sequence description.
> > >> This supports my contention that the author was not clear about what
> he
> > was doing.
> > >>
> > >> But even given the rule above, there are a couple of clear mistakes in
> > the sequence.
> > >> By any reasonable definition we should have a(11) = 907 and a(20) =
> 701.
> > >> The sequence needs to have its elements fixed, or be deaded.
> > >>
> > >>> -----Original Message-----
> > >>> From: SeqFan [mailto:seqfan-bounces at list.seqfan.eu] On Behalf Of
> Frank
> > >>> Adams-Watters
> > >>> Sent: Saturday, September 19, 2015 1:29 AM
> > >>> To: seqfan at list.seqfan.eu
> > >>> Subject: [seqfan] Re: A089755
> > >>>
> > >>> David: no, the definition is consistent. You are not understanding
> > what is
> > >>> meant by retaining leading zeros.
> > >>>
> > >>> After 13, the 1 is dropped, leaving 3. Since 1 digit numbers are
> > prohibited, we
> > >>> can't get just make 3 the next term; it has to be 31.
> > >>>
> > >>> After 103, the 1 is dropped and we have 03, which is two digits and
> > thus
> > >>> acceptable. This appears in the database as 3, because the OEIS
> > doesn't allow
> > >>> leading zeros; but it's "really" 03.
> > >>>
> > >>> After 03, we drop the leading 0, and get something starting with 3:
> > specifically
> > >>> 37.
> > >>>
> > >>> If I were to program it, which I probably won't, I would store the
> > sequence as
> > >>> strings instead of as numbers.
> > >>>
> > >>> This sequence is clearly the work of someone who, at least at that
> > time, did
> > >>> not understand how to use the empty string.
> > >>>
> > >>> Franklin T. Adams-Watters
> > >>>
> > >>> P.S. If someone can provide a better description, I'm fine with that.
> > >>>
> > >>> -----Original Message-----
> > >>> From: David Wilson <davidwwilson at comcast.net>
> > >>> To: 'Sequence Fanatics Discussion list' <seqfan at list.seqfan.eu>
> > >>> Sent: Sat, Sep 19, 2015 12:12 am
> > >>> Subject: [seqfan] Re: A089755
> > >>>
> > >>>
> > >>> A few notes on A089755 et al.(...)
> >
> > _______________________________________________
> >
> > Seqfan Mailing list - http://list.seqfan.eu/
> >
>
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