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 A218659 #8 Mar 10 2018 05:46:58 %S A218659 9,225,3249,50625,793881,12383361,193349025,3018953025,47135449449, %T A218659 735942652641,11490533873361,179405691966081,2801123686963449, %U A218659 43734921492423681,682848585990347841,10661553197658712449 %N A218659 Hilltop maps: number of n X 4 binary arrays indicating the locations of corresponding elements not exceeded by any king-move neighbor in a random 0..1 n X 4 array. %C A218659 Column 4 of A218663. %H A218659 R. H. Hardin, <a href="/A218659/b218659.txt">Table of n, a(n) for n = 1..210</a> %F A218659 Empirical: a(n) = 12*a(n-1) +45*a(n-2) +180*a(n-3) -27*a(n-4) -81*a(n-6). %F A218659 Empirical g.f.: 9*x*(1 - x)*(1 + 14*x + 30*x^2 + 18*x^3 + 9*x^4) / ((1 + 3*x + 9*x^2 - 9*x^3)*(1 - 15*x - 9*x^2 - 9*x^3)). - _Colin Barker_, Mar 10 2018 %e A218659 Some solutions for n=3: %e A218659 ..0..1..0..1....1..0..1..0....0..0..0..0....1..0..0..0....1..1..1..1 %e A218659 ..0..1..0..1....1..1..0..0....0..1..0..1....1..0..1..0....1..0..0..1 %e A218659 ..0..0..0..1....0..0..0..1....0..1..1..1....0..1..1..1....0..1..1..0 %Y A218659 Cf. A218663. %K A218659 nonn %O A218659 1,1 %A A218659 _R. H. Hardin_, Nov 04 2012