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%I #13 Dec 04 2023 16:44:24
%S 3,12,68,438,3054,22417,170610,1334316
%N Number of fixed n-polyominoids, allowing right-angled connections only ("hard" polyominoids).
%C Apparently, the definition of "hard" polyominoid in the Wikipedia article differs from the definition used here. Here, two squares are allowed to meet in a straight 180-degree connection provided that the structure be connected through right-angled ("hard") connections only; see A365654 for further details.
%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Polyominoid">Polyominoid</a>.
%H <a href="/index/Pol#polyominoes">Index entries for sequences related to polyominoes</a>.
%Y Cf. A075678 (polyominoids), A365654 (free).
%Y 13th and 17th row of A366767.
%K nonn,hard,more
%O 1,1
%A _Pontus von Brömssen_, Sep 17 2023