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%I M3289 #21 Jan 31 2022 01:26:44
%S 1,1,4,6,23,32,91
%N Number of n-dimensional crystal families.
%D H. Brown, R. Bülow, J. Neubüser, H. Wondratschek and H. Zassenhaus, Crystallographic Groups of Four-Dimensional Space. Wiley, NY, 1978, p. 52.
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H W. Plesken and T. Schulz, <a href="http://projecteuclid.org/euclid.em/1045604675">Counting crystallographic groups in low dimensions</a>, Experimental Mathematics, Volume 9 Issue 3 (2000), 321-478
%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Space_group">Space_group</a>
%Y Cf. A004027-A004031, A006226, A006227.
%K hard,nonn,nice
%O 0,3
%A _N. J. A. Sloane_
%E a(5)-a(6) from _Henry Bottomley_, Feb 03 2014
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