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%I #9 Dec 05 2014 03:00:07
%S 1,1,4,10,37,147,637,2823,13020,60649,286549,1364667,6547108,31586568
%N Number of free poly-IH18-tiles (holes allowed) with n cells.
%C Equivalently, polyhexes where two polyhexes are considered equivalent if and only if they are related by a translation, a rotation of order 3 or a reflection or glide reflection in a line perpendicular to the sides of the hexagons.
%D Branko Grünbaum and G. C. Shephard, Tilings and Patterns. W. H. Freeman, New York, 1987, Sections 6.2 and 9.4.
%Y Cf. A000228, A001207, A006535, A057973, A197549, A197550, A197552, A197553, A197554.
%K hard,nonn
%O 1,3
%A _Joseph Myers_, Oct 16 2011