# [seqfan] Re: Another surprising omission from OEIS

Jack Brennen jfb at brennen.net
Thu Nov 12 18:42:49 CET 2009

```Precisely.  The list of numbers which are repdigits in some base is most
certainly not a "base" sequence.

It's the list of numbers which can be expressed in the form:
a*(b^n-1)/(b-1), with n > 2, a > 0, b > a.

Andrew Weimholt wrote:
> On Thu, Nov 12, 2009 at 8:08 AM, Alonso Del Arte
> <alonso.delarte at gmail.com> wrote:
>> The title of this thread has bothered me since I read the first post in it.
>> I think the reason is that I don't find the omission of a keyword:base
>> sequence surprising at all. Most math amateurs, if they stick to it,
>> eventually lose interest in base sequences. Most professional mathematicians
>> probably feel that they must specialize in the topic of radix representation
>> if they're going to give it any significant portion of their time. Modular
>> arithmetic, on the other hand, is so fundamental to number theory that the
>> absence of the orderly numbers from the OEIS for so long I do find genuinely
>> surprising. Well, that's just my opinion, for what it's worth.
>>
>> Al
>
> I don't find "base" sequences as interesting either, especially when
> only one base (usually base 10) is considered.
> I feel that if you are going to look for numbers with certain
> syntactical properties (such as repdigits, palindromes, etc) then why
> not do the search in all bases.
>
> By the way, my interpretation of the "base" keyword (Neil, correct me
> if I am wrong) is that it applies to sequences which use a single base
> in their definition (so that if you change the base, the sequence will
> contain a different set of terms). Sequences which cover all the bases
> are not really "base" sequences (which is why I didn't add the "base"
> keyword to these submissions).
> The OEIS help file for keywords says "base: dependent on base used for
> sequence", which seems to support my interpretation.
>
> Andrew
>
>
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```