[seqfan] Re: Help with A028247 Number of T-frame polyominoes with n cells

[John Mason]

Thanks for everyone's help. That got me through to a(6).
But now, instead of a(7)=10, I'm getting 11. Which of these is wrong?
(I am using the following condition: the polyomino must be board-pile,
convex, have a complete top row (extends over the entire width), and a
bottom row that starts a bit to the right of the top row and finishes a bit
to the left)

1.
OOO
OOO
_O_

2.
OOOOO
_OO__

3.
OOOO
OO__
_O__

4.
OOOO
_OO_
_O__

5.
OOO
OO_
_O_
_O_

6.
OOOOOO
_O____

7.
OOOOOO
__O___

8.
OOOOO
_O___
_O___

9.
OOOOO
__O__
__O__

10.
OOOO
_O__
_O__
_O__

11.
OOO
_O_
_O_
_O_
_O_

On Wed, Feb 1, 2023 at 5:38 AM Don Reble via SeqFan <seqfan at list.seqfan.eu>
wrote:

> > XXX
> > XX.
> > .X.
>
> > ...polyominoes which are integral rectangles with integral notches cut
> > from two adjacent corners.
>
>     I like that take, yielding sequence
>         0,0,0,1,2,6,10,18,27,42,55,80,101,133,163,211,246,308,353,432,...
>     but I get a(8)=18 instead of 19, etc. Did I miss one?
>
> .XXX. .XX... ..XX.. .X..... ..X.... ...X...
> XXXXX XXXXXX XXXXXX XXXXXXX XXXXXXX XXXXXXX
>
> .XX. .X... .X.... ..X...
> .XX. XX... .X.... ..X...
> XXXX XXXXX XXXXXX XXXXXX
>
> .X. .X. .X.. .X... ..X..
> XX. .X. .X.. .X... ..X..
> XX. XXX XX.. .X... ..X..
> XXX XXX XXXX XXXXX XXXXX
>
> .X. .X..
> .X. .X..
> .X. .X..
> XX. .X..
> XXX XXXX
>
> .X.
> .X.
> .X.
> .X.
> .X.
> XXX
>
> --
> Don Reble  djr at nk.ca
>
>
> --
> Seqfan Mailing list - http://list.seqfan.eu/
>