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Diagonally symmetric (about diagonal 2) 2n-celled polyominoes with 1 hole.
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%I #13 Jan 16 2023 11:16:29

%S 1,1,5,7,21,30,88,116,336,439,1271,1639,4713,6088,17452

%N Diagonally symmetric (about diagonal 2) 2n-celled polyominoes with 1 hole.

%C The sequence refers to polyominoes with one hole and both diagonal symmetries but no other. - _John Mason_, Jan 16 2023

%H Tomás Oliveira e Silva, <a href="http://sweet.ua.pt/tos/animals.html">Enumeration of polyominoes</a>

%Y Cf. A056882.

%K nonn,more

%O 6,3

%A _N. J. A. Sloane_, Sep 05 2000

%E a(15)-a(20) from _John Mason_, Jan 16 2023