0,2

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

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.

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.

T. Janssen, Crystallographic Groups. North-Holland, Amsterdam, 1973, p. 73.

W. Plesken and T. Schulz, Counting crystallographic groups in low dimensions, Experimental Mathematics, 9 (No. 3, 2000), 407-411.

W. Plesken and T. Schulz, CARAT Homepage

Experimental Mathematics, Home Page

Cf. A004027, A004029.

Sequence in context: A083099 A032095 A151019 this_sequence A080668 A062453 A036369

Adjacent sequences: A004025 A004026 A004027 this_sequence A004029 A004030 A004031

nonn,hard,nice

N. J. A. Sloane (njas(AT)research.att.com).