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 A157231 #14 Oct 01 2018 03:07:44 %S A157231 0,0,0,0,0,1,1,1,2,2,2,3,2,4,4,4,3,7,4,6,6,7,5,8,6,8,8,9,6,14,7,10,10, %T A157231 11,10,15,8,13,12,14,9,20,10,15,16,16,11,20,13,20,16,18,12,25,16,20, %U A157231 18,20,14,30,14,22,22,22,18,32,16,24,22,32,17,32,17 %N A157231 Number of primitive inequivalent oblique sublattices of square lattice of index n (equivalence and symmetry of sublattices are determined using parent lattice symmetries). %H A157231 Andrey Zabolotskiy, <a href="/A157231/b157231.txt">Table of n, a(n) for n = 1..5000</a> %H A157231 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 5.] %F A157231 a(n) = (A001615(n) - A019590(n) - 2 * (A157228(n) + A157226(n) + A157230(n))) / 4. - _Andrey Zabolotskiy_, May 09 2018 %Y A157231 Cf. A145393 (all sublattices of the square lattice), A019590, A157228, A157226, A157230, A001615, A304182. %K A157231 nonn %O A157231 1,9 %A A157231 _N. J. A. Sloane_, Feb 25 2009 %E A157231 New name and more terms from _Andrey Zabolotskiy_, May 09 2018