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 A157224 #17 May 04 2021 10:44:18 %S A157224 0,1,2,3,2,6,4,6,6,8,6,12,6,12,12,12,8,18,10,18,16,18,12,24,14,20,18, %T A157224 24,14,36,16,24,24,26,24,36,18,30,28,36,20,48,22,36,36,36,24,48,28,44, %U A157224 36,42,26,54,36,48,40,44,30,72,30,48,48,48,40,72,34,54 %N A157224 Number of primitive inequivalent (up to Pi/2 rotation) nonsquare sublattices of square lattice of index n. %H A157224 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 A157224 a(n) = (A001615(n) - A000089(n))/2. - _Andrey Zabolotskiy_, May 09 2018 %Y A157224 Cf. A000089 (primitive square sublattices), A002654 (all square sublattices), A145392 (all sublattices), A001615, A304182. %K A157224 nonn %O A157224 1,3 %A A157224 _N. J. A. Sloane_, Feb 25 2009 %E A157224 New name and more terms from _Andrey Zabolotskiy_, May 09 2018