# [seqfan] Re: A065843 and their crossrefs.

Neil Sloane njasloane at gmail.com
Sat Apr 23 18:06:51 CEST 2016

```David, Yes, there does seem to be a problem with all those sequences!
It looks like they all need editing.
The definitions seem to be both incomplete and wrong

Could someone write a quick program to check A065843, A065844, etc?
Fix the base b (b=2 for A065843 (as David says, the present definition
seems wrong), b=3 for A065844, etc)
Fix n. Look at all words w of length n in base b. For each w, find
how many primes of length n you can get by permuting the digits of w. Then
a(n) = max over w of this number.

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.
Email: njasloane at gmail.com

On Fri, Apr 22, 2016 at 7:49 PM, David Corneth <davidacorneth at gmail.com>
wrote:

> I guess priority low.
> The sequences mentioned in the title are quite similar.
> A065843 has name
> 'Let u be any string of n digits from {0,...,2}; let f(u) = number of
> distinct primes, not beginning with 0, formed by permuting the digits of u;
> then a(n) = max_u f(u).'.
> The comment is about binary numbers. Should then the digits come from {0,
> 1}? If so then I guess this sequence and the 10 crossrefs in it should be
> edited at some  point to fix it. I could do it but I can only have 7 drafts
> at a time and I have 3 other drafts already. Should these edits be made?
>
> Furthermore, for A065843, I'd write the example as
> 'a(4)=2 because 1011 and 1101 in base-2-notation are primes. No other set
> of four-digit-numbers in binary with the same digitsum have the same number
> of primes in them.'
>
> Could some-one enlighten my here?
>
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>
```