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 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,8 LINKS Table of n, a(n) for n=1..27. D. H. Redelmeier, Counting polyominoes: yet another attack, Discrete Math., 36 (1981), 191-203. FORMULA a(n) = A348402(n) - A348404(n). 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). Sequence in context: A262444 A372559 A109755 * A005254 A272265 A191796 Adjacent sequences: A348400 A348401 A348402 * A348404 A348405 A348406 KEYWORD nonn,more AUTHOR John Mason, Oct 18 2021 STATUS approved

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Last modified August 4 13:44 EDT 2024. Contains 374923 sequences. (Running on oeis4.)