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Number of polyiamonds with 2n cells that tile the plane both by translation and by 180-degree rotation (Conway criterion).
10

%I #11 Dec 05 2014 02:42:54

%S 1,2,8,24,61,269,501,2121,4709,14978,26675,123081,179707,660366,

%T 1479114

%N Number of polyiamonds with 2n cells that tile the plane both by translation and by 180-degree rotation (Conway criterion).

%C Polyiamonds with an odd number of cells have different numbers of triangles with the two orientations and so cannot tile by translation.

%D Branko Grünbaum and G. C. Shephard, Tilings and Patterns. W. H. Freeman, New York, 1987, Section 9.4.

%H Joseph Myers, <a href="http://www.polyomino.org.uk/mathematics/polyform-tiling/">Polyiamond tiling</a>

%Y Cf. A071332, A075216, A075217, A075219, A075220, A075221, A075222, A075223, A075224, A075200, A075209.

%K hard,nonn

%O 1,2

%A _Joseph Myers_, Sep 08 2002

%E More terms from _Joseph Myers_, Nov 11 2003

%E a(15) (30-iamonds) from _Joseph Myers_, Nov 21 2010