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 A047937 #25 Dec 11 2023 18:18:09
%S A047937 1,2,6,140,16456,8390720,17179934976,140737496748032,
%T A047937 4611686019501162496,604462909807864344215552,
%U A047937 316912650057057631849169289216,664613997892457937028364283517337600,5575186299632655785385110159782842147536896,187072209578355573530071668259090783437390809661440
%N A047937 Number of 2-colorings of an n X n grid, up to rotational symmetry.
%C A047937 Cycle index = 1/4(s_1^(n^2)+ 2 s_4^floor(n^2/4)s_1^(n mod 2)+s_2^floor(n^2/2)s_1^(n mod 2)). - _Geoffrey Critzer_, Oct 28 2011
%H A047937 Andrew Howroyd, <a href="/A047937/b047937.txt">Table of n, a(n) for n = 0..50</a>
%H A047937 Peter Kagey, <a href="/A047937/a047937.pdf">Illustration of a(3)=140</a>
%H A047937 Peter Kagey and William Keehn, <a href="https://arxiv.org/abs/2311.13072">Counting tilings of the n X m grid, cylinder, and torus</a>, arXiv:2311.13072 [math.CO], 2023.
%F A047937 a(n) = (m^(n^2) + 2*m^((n^2 + 3*(n mod 2))/4) + m^((n^2 + (n mod 2))/2))/4, with m = 2.
%e A047937 a(2)=6 from
%e A047937 00 10 11 10 11 11
%e A047937 00 00 00 01 10 11
%t A047937 Table[(2^(n^2)+2*2^Floor[n^2/4]*2^Mod[n,2]+2^Floor[n^2/2]*2^Mod[n,2])/4,{n,0,10}] (* _Geoffrey Critzer_, Oct 28 2011 *)
%Y A047937 Column k=2 of A343095.
%Y A047937 Other columns are A047938, A047939, A047940, A047941, A047942, A047943, A047944, A047945.
%Y A047937 Cf. A054247.
%K A047937 nonn,easy,nice
%O A047937 0,2
%A A047937 _Rob Pratt_
%E A047937 Terms a(12) and beyond from _Andrew Howroyd_, Apr 14 2021