[seqfan] Re: Two-fold symmetry sequence

[Frederick Schneider]

Sorry for the omission, I mean rotational symmetry.

And, polyominoes is the term I should have used.

Thanks

On Mon, Dec 29, 2008 at 4:12 PM, <franktaw at netscape.net> wrote:

> First of all, these are called "polyominoes".  "Shape" is a far
> more general term; it would include, for example, squares
> joined only at a corner.
>
> From your web site, it appears that you are looking only for
> 2-fold rotational symmetry.  2-fold symmetry includes also
> reflective symmetries, such as are possessed by
>
> OO
> O
>
> and
>
> OOO
>  O
>
> amongst others.
>
> The number of polyominoes with reflective symmetry is A030227.
> I don't think your sequence is in the database, although I'm not
> entirely certain.
>
> Franklin T. Adams-Watters
>
> -----Original Message-----
> From: Frederick Schneider <frederick.william.schneider at gmail.com>
>
> Sorry, that should be:
>
> 1,1,1,3,3,7
>
> On Mon, Dec 29, 2008 at 2:28 PM, Frederick Schneider <
> frederick.william.schneider at gmail.com> wrote:
>
> > Hello,
> >
> > I tried to find but didn't see the number of distinct 2-fold symmetric
> > shapes that can be made from n squares.
> >
> > Starting from n=1 :  1,1,1,3,3,6
> >
> > Here's an image explaining what I mean:
> >
> > http://www.bosola.org/grandpa/imgs/2-foldSymmetry.jpg
> >
> > Has anyone seen a similar sequence?  If not, I'll try to extend this
> at
> > least a few terms out.
> >
> > Thanks,
> > Fred
> >
> >
>
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