

A348403


Number of chiral pairs of polyomino rings of length 2n with twofold rotational symmetry.


3



0, 0, 0, 0, 0, 0, 1, 3, 9, 21, 51, 117, 262, 598, 1307, 2987, 6456, 14752, 31859, 72839, 157611, 360472, 782802, 1791140, 3904323, 8936996, 19553272
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OFFSET

1,8


LINKS



FORMULA



EXAMPLE

a(7)=1 because of:
OOOO
O..OO
OO..O
.OOOO


CROSSREFS

Cf. A348402 (all unoriented), A348404 (achiral), A324407 (unoriented with fourfold rotational symmetry), A324408 (chiral with fourfold rotational symmetry), A324409 (achiral with fourfold rotational symmetry).


KEYWORD

nonn,more


AUTHOR



STATUS

approved



