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%I #8 Nov 14 2021 07:25:55
%S 0,0,0,0,0,0,1,3,9,21,51,117,262,598,1307,2987,6456,14752,31859,72839,
%T 157611,360472,782802,1791140,3904323,8936996,19553272
%N Number of chiral pairs of polyomino rings of length 2n with twofold rotational symmetry.
%H D. H. Redelmeier, <a href="http://dx.doi.org/10.1016/0012-365X(81)90237-5">Counting polyominoes: yet another attack</a>, Discrete Math., 36 (1981), 191-203.
%F a(n) = A348402(n) - A348404(n).
%e a(7)=1 because of:
%e OOOO
%e O..OO
%e OO..O
%e .OOOO
%Y Cf. A348402 (all unoriented), A348404 (achiral), A324407 (unoriented with fourfold rotational symmetry), A324408 (chiral with fourfold rotational symmetry), A324409 (achiral with fourfold rotational symmetry).
%K nonn,more
%O 1,8
%A _John Mason_, Oct 18 2021
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