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

John Mason masonmilan33 at gmail.com
Wed Feb 1 15:32:33 CET 2023

```Answering my own question, by David's definition, my (4) is wrong.
john

On Wed, Feb 1, 2023 at 10:44 AM John Mason <masonmilan33 at gmail.com> wrote:

> 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/
>>
>
```