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 A157227 #13 May 09 2018 16:44:12 %S A157227 0,1,1,2,2,4,2,4,4,6,4,8,4,8,8,8,6,12,6,12,10,12,8,16,10,14,12,16,10, %T A157227 24,10,16,16,18,16,24,12,20,18,24,14,32,14,24,24,24,16,32,18,30,24,28, %U A157227 18,36,24,32,26,30,20,48,20,32,32,32,28,48,22,36,32,48 %N A157227 Number of primitive inequivalent (up to Pi/3 rotation) non-hexagonal sublattices of hexagonal (triangular) lattice of index n. %H A157227 John S. Rutherford, <a href="http://dx.doi.org/10.1107/S010876730804333X">Sublattice enumeration. IV. Equivalence classes of plane sublattices by parent Patterson symmetry and colour lattice group type</a>, Acta Cryst. (2009). A65, 156-163. [See Table 4.] %F A157227 a(n) = (A001615(n) - A000086(n))/3. - _Andrey Zabolotskiy_, May 09 2018 %Y A157227 Cf. A000086 (primitive hexagonal sublattices), A002324 (all hexagonal sublattices), A145394 (all sublattices), A001615, A304182. %K A157227 nonn %O A157227 1,4 %A A157227 _N. J. A. Sloane_, Feb 25 2009 %E A157227 New name and more terms from _Andrey Zabolotskiy_, May 09 2018