%I A004028 M1965
%S A004028 1,2,10,32,227,955,7104
%N A004028 Geometric n-dimensional crystal classes.
%D A004028 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A004028 H. Brown, R. B\"{u}low, J. Neub\"{u}ser, H. Wondratschek and H. Zassenhaus, 
               Crystallographic Groups of Four-Dimensional Space. Wiley, NY, 1978, 
               p. 52.
%D A004028 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 A004028 T. Janssen, Crystallographic Groups. North-Holland, Amsterdam, 1973, 
               p. 73.
%D A004028 W. Plesken and T. Schulz, Counting crystallographic groups in low dimensions, 
               Experimental Mathematics, 9 (No. 3, 2000), 407-411.
%H A004028 W. Plesken and T. Schulz, <a href="http://wwwb.math.rwth-aachen.de/carat/
               ">CARAT Homepage</a>
%H A004028 Experimental Mathematics, <a href="http://www.expmath.org/">Home Page</
               a>
%Y A004028 Cf. A004027, A004029.
%Y A004028 Sequence in context: A083099 A032095 A151019 this_sequence A080668 A062453 
               A036369
%Y A004028 Adjacent sequences: A004025 A004026 A004027 this_sequence A004029 A004030 
               A004031
%K A004028 nonn,hard,nice
%O A004028 0,2
%A A004028 N. J. A. Sloane (njas(AT)research.att.com).