[seqfan] Re: A347521 Number of polyominoes with n cells formed by coordinates that are not coprime

Peter Kagey peterkagey at gmail.com
Wed Sep 14 15:19:27 CEST 2022

Hi John,

See the attached PDF: http://oeis.org/A347521/a347521.pdf

Here’s a guess: it looks like only the “T” tetromino is included for a(4), as you can position it in the plane such that all of it’s cell coordinates have coprime x- and y-coordinates, but any adjacent coordinate does not have this property.

On Sep 14, 2022 at 5:28 AM -0700, John Mason <masonmilan33 at gmail.com>, wrote:
> Hi sequence fans
> I have looked at this sequence but I don't know how it works.
> Could anyone maybe give an explanation of, e.g., a(4)=1, say by
> illustrating why 4 of the 5 tetrominoes are excluded and just 1 is included?
> I would contact the author but his wiki page says no email address is
> available.
> Thanks
> john
> --
> Seqfan Mailing list - http://list.seqfan.eu/

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