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 A218658 #8 Mar 10 2018 05:46:52 %S A218658 5,57,417,3249,25533,199489,1560161,12202673,95434773,746388537, %T A218658 5837454753,45654295713,357058903853,2792531543489,21840184444225, %U A218658 170810481722657,1335896257560101,10447946710663673,81712625405191841 %N A218658 Hilltop maps: number of n X 3 binary arrays indicating the locations of corresponding elements not exceeded by any king-move neighbor in a random 0..1 n X 3 array. %C A218658 Column 3 of A218663. %H A218658 R. H. Hardin, <a href="/A218658/b218658.txt">Table of n, a(n) for n = 1..210</a> %F A218658 Empirical: a(n) = 6*a(n-1) + 11*a(n-2) + 26*a(n-3) - 5*a(n-4) - 5*a(n-6). %F A218658 Empirical g.f.: x*(5 + 27*x + 20*x^2 - 10*x^3 - 5*x^4 - 5*x^5) / (1 - 6*x - 11*x^2 - 26*x^3 + 5*x^4 + 5*x^6). - _Colin Barker_, Mar 10 2018 %e A218658 Some solutions for n=3: %e A218658 ..0..0..1....1..1..0....1..0..0....1..1..0....1..0..0....0..1..0....1..1..1 %e A218658 ..1..1..1....1..1..1....0..0..1....1..0..0....1..0..1....0..1..1....0..1..0 %e A218658 ..1..0..0....1..1..0....0..1..0....0..1..1....0..1..0....0..1..0....1..1..1 %Y A218658 Cf. A218663. %K A218658 nonn %O A218658 1,1 %A A218658 _R. H. Hardin_, Nov 04 2012