# [seqfan] Re: a(n) | n

Neil Sloane njasloane at gmail.com
Fri Jan 26 16:37:21 CET 2018

```Franklin,  Nice list of pairs!  I'll create an Index entry for "a(n)
divides n",
which will be part of the first section (Aa) of the Index.

If you (or anyone else) have further examples, you
can edit that Index page (but remember the oeis wiki requires

of those pairs, I agree it is a good idea - go ahead and do it

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 Thu, Jan 25, 2018 at 2:36 PM, Frank Adams-Watters via SeqFan <
seqfan at list.seqfan.eu> wrote:

> I've been looking recently at sequences where a(n) divides n for every n >
> 0.
>
> These come naturally in pairs, whose element-wise product is n.
>
> Here's a list, which is by no means complete:
>
> A000012 * A000027
> A000034 * A026741
> A000265 * A006519
> A003557 * A007947
> A006530 * A052126
> A007913 * A008833
> A020639 * A032742
> A028233 * A028234
> A033676 * A033677
> A034699 * A284600
> A060789 * A089128
> A065330 * A065331
> A060775 * A140271
> A122377 * A298734
>
> (A298734 I have just submitted.)
>
> It seems to me that this should be documented somewhere in the OEIS, but
> I'm not sure where. (Maybe in the index file somewhere?)
>
> Preserving this property is for me one good reason to have a(1) = 1 in
> sequences like A020439 (least prime factor) where a(1) is otherwise
> undefined.
>