This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A071881 #13 Oct 26 2018 02:47:33 %S A071881 1,1,1,1,3,222 %N A071881 Number of different primitive polyhedral types of Voronoi regions of n-dimensional point lattices. %C A071881 Or, number of combinatorial types of primitive n-dimensional parallelohedra. %C A071881 Or, number of combinatorial types of Delaunay [Delone] decompositions of R^n. %C A071881 Voronoi proved a(n) finite. %D A071881 E. S. Barnes and N. J. A. Sloane, "The optimal lattice quantizer in three dimensions," SIAM J. Algebraic Discrete Methods vol. 4 (Mar. 1983) 30-41. %D A071881 J. H. Conway, The Sensual Quadratic Form. %D A071881 J. H. Conway and N. J. A. Sloane, Low-Dimensional Lattices VI: Voronoi Reduction of Three-Dimensional Lattices, Proc. Royal Soc. London, Series A, 436 (1992), 55-68. %D A071881 P. Engel, Investigations of parallelohedra in Rd, in: Voronoi's Impact on Modern Science, P. Engel and H. Syta (eds), Institute of Mathematics, Kyiv, 1998, Vol. 2, pp. 2260. %D A071881 P. Engel, The contraction types of parallelohedra in E^5, Acta Crystallogr., A56 (2000), 491-496. %D A071881 P. Engel and V. Grishukhin, There are exactly 222 L-types of primitive five-dimensional lattices. European J. Combin. 23 (2002), 275-279. %D A071881 S. S. Ryshkov and E. P. Baranovskii, "C-types of n-dimensional lattices and 5-dimensional primitive parellohedra (with an application to the theory of coverings)" Proc. Steklov Inst. Math., 137 (1975) Trudy Mat. Inst. Steklov., 137 (1975) %D A071881 M. I. Stogrin, Regular Dirichlet-Voronoi partitions for the second triclinic group, Trudy Matematicheskogo Instituta imeni V. A. Steklova, 123 (1973) = Proceedings of the Steklov Institute of Mathematics, 123 (1973). %D A071881 G. F. Voronoi, "Studies of primitive parallelotopes", Collected Works, 2, Kiev (1952) pp. 239-368 (In Russian). %H A071881 Mathieu Dutour Sikiric, Alexey Garber, <a href="https://arxiv.org/abs/1810.10911">Periodic triangulations of Z^n</a>, arXiv:1810.10911 [math.CO], 2018. %H A071881 Russian Math. Encyclopedia, <a href="http://eom.springer.de/V/v096920.htm">Voronoi</a> %H A071881 Achill Schuermann and Frank Vallentin, <a href="http://arxiv.org/abs/math/0403272">Computational Approaches to Lattice Packing and Covering Problems</a>, arXiv:math/0403272v3 [math.MG], 2004-2005. %e A071881 a(2)=1 because the hexagon is the only allowed type (quadrilateral is a degenerate hexagon). a(3)=1 because the truncated octahedron is the only allowed type. - _Warren D. Smith_, Dec 27 2007 %Y A071881 Cf. A071880, A071882. %K A071881 nonn,hard,nice %O A071881 0,5 %A A071881 _N. J. A. Sloane_, Jun 10 2002, Jul 03 2008