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Number of fixed n-polyominoids, allowing right-angled connections only ("hard" polyominoids).
5

%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