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 A226304 #12 Nov 04 2019 02:19:11 %S A226304 1,1,2,1,1,2,1,1,2,4,0,2,1,0,1,2,2,-2,2,1,0,1,2,2,4,-2,4,0,2,-2,2,1,0, %T A226304 1,1,2,3,4,-2,2,0,4,-2,2,-2,2,1,0,1,1,2,3,4,6,-2,6,0,8,-2,4,-4,6,-2,4, %U A226304 -2,2,-2,2,1,-1,1,0,1,1,1,2,2,-6,6,-2,6,-6,4,-4,6,-6,6,-4,4,-4,2,1,-1,1,0,1,1,1,2,2,4,-8,10,-4,10,-8,8,-8,10,-10,12,-8,10,-12,10,-6,6,-6,6,-4,4,-4,2 %N A226304 Irregular triangle read by rows: coefficients of certain polynomials P_n(x) arising in the enumeration of tatami mat coverings. %C A226304 See Erickson-Ruskey for precise definition. The polynomials P_n(x) are described as "mysterious". %H A226304 Alejandro Erickson, Frank Ruskey, <a href="http://arxiv.org/abs/1304.0070">Enumerating maximal tatami mat coverings of square grids with v vertical dominoes</a>, arXiv:1304.0070 [math.CO], 2013. %e A226304 Triangle begins: %e A226304 1 %e A226304 1,2 %e A226304 1,1,2 %e A226304 1,1,2,4,0,2 %e A226304 1,0,1,2,2,-2,2 %e A226304 1,0,1,2,2,4,-2,4,0,2,-2,2 %e A226304 1,0,1,1,2,3,4,-2,2,0,4,-2,2,-2,2 %e A226304 1,0,1,1,2,3,4,6,-2,6,0,8,-2,4,-4,6,-2,4,-2,2,-2,2 %e A226304 1,-1,1,0,1,1,1,2,2,-6,6,-2,6,-6,4,-4,6,-6,6,-4,4,-4,2 %e A226304 1,-1,1,0,1,1,1,2,2,4,-8,10,-4,10,-8,8,-8,10,-10,12,-8,10,-12,10,-6,6,-6,6,-4,4,-4,2 %e A226304 ... %Y A226304 Cf. A226302, A226303. %K A226304 sign,tabf %O A226304 2,3 %A A226304 _N. J. A. Sloane_, Jun 06 2013