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 A055900 #6 Aug 17 2021 02:48:44 %S A055900 1,9,51,209,696,1980,5000,11475,24375,48545,91581,164934,285376, %T A055900 476784,772416,1217610,1873125,2819025,4159375,6027615,8592936, %U A055900 12067484,16714776,22859109,30896411,41306265,54665625,71663900 %N A055900 Column 4 of triangle A055898. %H A055900 A. J. Guttmann, <a href="https://doi.org/10.1016/S0012-365X(99)00262-9">Indicators of solvability for lattice models</a>, Discrete Math., 217 (2000), 167-189 (H_4 for square lattices of Section 6). %F A055900 G.f.: x^4*(1+3x+9x^2+9x^3+9x^4+3x^5+x^6)/((1-x)^9*(1+x)^3). %Y A055900 Cf. A055898. %K A055900 nonn %O A055900 4,2 %A A055900 _Christian G. Bower_, Jun 13 2000