%I #10 May 01 2023 10:01:46
%S 0,0,0,1,0,0,2,2,1,6,9,11,21,49,69,117,249,427
%N 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 George Sicherman, <a href="https://sicherman.net/nunitary/nunitarya.html">Catalogue of Almost Unitary Polyominoes</a>
%e a(4)=1 because of:
%e O
%e OO
%e O
%Y Cf. A245660, A362709.
%K nonn,hard,more
%O 1,7
%A _John Mason_, Apr 30 2023