# [seqfan] Re: A089755

Allan Wechsler acwacw at gmail.com
Sun Sep 20 00:17:34 CEST 2015

```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
> >>> 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.
> >>>
> >>>
> >>> 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/
>

```