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 A018803 #21 Feb 14 2019 09:23:40 %S A018803 1,2,14,276,10980,781712,58339148,3066831440,58170992144,313031791856, %T A018803 109957124552,5020721992,3980056,1140264,232228 %N A018803 Number of ways to color cells of an n X n square with 2 colors so that no subsquare of side > 1 has all corners same color. %C A018803 There is no solution for a 15 X 15 (or larger) square. - _Sean A. Irvine_, Feb 13 2019 %H A018803 R. Bacher and S. Eliahou, <a href="https://www.cs.umd.edu/~gasarch/TOPICS/vdw/2colsq.pdf">Extremal binary matrices without constant 2-squares</a> (see p. 11). %H A018803 R. Bacher and S. Eliahou, <a href="https://dx.doi.org/10.4310/JOC.2010.v1.n1.a6">Extremal binary matrices without constant 2-squares</a>, The Electronic Journal of Combinatorics, Open Journal Systems, 2010, 1 (1), pp.77-100. See p. 87. %Y A018803 Main diagonal of A255256. %K A018803 nonn,fini,full %O A018803 0,2 %A A018803 _David W. Wilson_ %E A018803 a(0)=1 from _Alois P. Heinz_, Feb 19 2015 %E A018803 More terms from Bacher and Eliahou paper added by _Sean A. Irvine_, Feb 13 2019