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

[Arthur O'Dwyer]

I also have no idea, but by analogy to "U-frame" and "Z-frame" informally
specified in https://doi.org/10.1016/0097-3165(91)90013-7 (authored by the
same author as the sequence: Anne Fontaine), I would expect the count to
start as follows: either 1,2,5,7,13,... or 1,3,7,12,19,...
But instead, it goes 1, 2, 6, 10, 19, 28, 44, 60.

For n=4: 1 T-frame polyomino
ooo
.o.
For n=5: 2 free T-frame polyominoes (3 one-sided)
ooo oooo
.o. .o..
.o.
For n=6: 5 free T-frame polyominoes (7 one-sided)
ooo oooo oooo ooooo ooooo
.o. .o.. .oo. .o... ..o..
.o. .o..
.o.
For n=7: 7 free T-frame polyominoes (12 one-sided)
ooo oooo ooooo ooooo oooooo oooooo ooo
.o. .o.. .oo.. .o... .o.... ..o... ooo
.o. .o..       .o...               .o.
.o. .o..
.o.
For n=8: 13 free T-frame polyominoes (19 one-sided)
ooo oooo oooo ooooo ooooo ooooo oooooo oooooo oooooo ooooooo ooooooo
ooooooo ooo
.o. .o.. .oo. .ooo. .o... ..o.. .o.... ..o... ..oo.. .o..... ..o....
...o... ooo
.o. .o.. .oo.       .o... ..o.. .o.... ..o...
  .o.
.o. .o..            .o... ..o..
  .o.
.o. .o..
.o.


On Tue, Jan 31, 2023 at 11:13 AM Michel Marcus <michel.marcus183 at gmail.com>
wrote:

> There are U-frames in https://doi.org/10.1016/0097-3165(91)90013-7.
> Best .
> MM
>
> Le mar. 31 janv. 2023 à 16:12, John Mason <masonmilan33 at gmail.com> a
> écrit :
>
> > Hi sequence fans
> > Does anyone know what a T-frame polyomino is?
> > I tried writing to the email address given in the sequence but to no
> avail.
> > I tried identifying polyominoes that look like a T but for a(6) I found
> > only 5.
> > Any ideas?
> > Thanks
> > john
> >
> > --
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> >
>
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