%I A006226 M1916
%S A006226 1,2,9,18,118,239,1594
%N A006226 Number of abstract n-dimensional crystallographic point groups.
%D A006226 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A006226 P. Engel, ``Geometric crystallography,'' in P. M. Gruber and J. M. Wills, 
               editors, Handbook of Convex Geometry. North-Holland, Amsterdam, Vol. 
               B, pp. 989-1041.
%D A006226 A. C. Hurley, Finite rotation groups and crystal classes in four dimensions. 
               Proc. Cambridge Philos. Soc. 47, (1951). 650-661.
%D A006226 A. C. Hurley, Crystal Classes of Four-Dimensional Space R4, Acta Crystallog., 
               22 (1967), see especially p. 605.
%D A006226 T. Janssen, Crystallographic Groups. North-Holland, Amsterdam, 1973, 
               p. 73.
%D A006226 W. Plesken and T. Schulz, Counting crystallographic groups in low dimensions, 
               Experimental Mathematics, 9 (No. 3, 2000), 407-411.
%H A006226 W. Plesken and T. Schulz, <a href="http://wwwb.math.rwth-aachen.de/carat/
               ">CARAT Homepage</a>
%H A006226 Experimental Mathematics, <a href="http://www.expmath.org/">Home Page</
               a>
%Y A006226 Cf. A004027, A004028, A004029.
%Y A006226 Sequence in context: A037421 A083423 A068978 this_sequence A109298 A075537 
               A075340
%Y A006226 Adjacent sequences: A006223 A006224 A006225 this_sequence A006227 A006228 
               A006229
%K A006226 hard,nonn,nice
%O A006226 1,2
%A A006226 N. J. A. Sloane (njas(AT)research.att.com).
%E A006226 Two more terms from W. Plesken and T. Schulz (tilman(AT)momo.math.rwth-aachen.de), 
               Feb 27, 2001.