%N Number of poly-IH73-tiles (holes allowed) with n cells.
%C Originally from Vicher's table, which lists this as "Puzzle 3".
%C Isohedral tiling IH73 (see Figure 6.2.4 of Grünbaum and Shephard) is obtained from the regular square tiling by replacing the edges of each square by symmetric curves bulging alternately inwards and outwards, so that each modified square now has a rotation of order two and reflections in horizontal and vertical axes as symmetries but no longer has rotations of order four or diagonal reflections as symmetries. - Joseph Myers, Oct 08 2011
%D Branko Grünbaum and G. C. Shephard, Tilings and Patterns. W. H. Freeman, New York, 1987, Sections 6.2 and 9.4.
%H M. Keller, <a href="http://www.solitairelaboratory.com/polyenum.html">Counting Polyforms</a>
%H M. Vicher, <a href="http://www.vicher.cz/puzzle/polyforms.htm">Polyforms</a>
%A _James A. Sellers_, Aug 28 2000
%E Edited by _T. D. Noe_, Apr 09 2009
%E Edited and a(11)-a(16) by _Joseph Myers_, Oct 08 2011