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

John Mason masonmilan33 at gmail.com
Wed Sep 14 14:28:00 CEST 2022

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

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