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A362708 a(n) is the number of almost unitary polyominoes of size n. An almost unitary polyomino is one in which all but 1 of its perimeter walls have length 1.

%I A362708 #10 May 01 2023 10:01:46
%S A362708 0,0,0,1,0,0,2,2,1,6,9,11,21,49,69,117,249,427
%N A362708 a(n) is the number of almost unitary polyominoes of size n. An almost unitary polyomino is one in which all but 1 of its perimeter walls have length 1.
%H A362708 George Sicherman, <a href="https://sicherman.net/nunitary/nunitarya.html">Catalogue of Almost Unitary Polyominoes</a>
%e A362708 a(4)=1 because of:
%e A362708   O
%e A362708   OO
%e A362708   O
%Y A362708 Cf. A245660, A362709.
%K A362708 nonn,hard,more
%O A362708 1,7
%A A362708 _John Mason_, Apr 30 2023