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 A228681 #11 Sep 12 2018 10:04:55 %S A228681 21,217,2529,28977,333517,3837761,44171841,508425617,5852202757, %T A228681 67361890809,775372578689,8924976046401,102731553583965, %U A228681 1182498825731233,13611237290882689,156673123529460833,1803397245448244085 %N A228681 Number of n X 6 binary arrays with no two ones adjacent horizontally, diagonally or antidiagonally. %H A228681 R. H. Hardin, <a href="/A228681/b228681.txt">Table of n, a(n) for n = 1..210</a> %F A228681 Empirical: a(n) = 14*a(n-1) - 17*a(n-2) - 142*a(n-3) + 59*a(n-4) + 352*a(n-5) + 103*a(n-6) - 48*a(n-7). %F A228681 Empirical g.f.: x*(21 - 77*x - 152*x^2 + 242*x^3 + 407*x^4 + 55*x^5 - 48*x^6) / (1 - 14*x + 17*x^2 + 142*x^3 - 59*x^4 - 352*x^5 - 103*x^6 + 48*x^7). - _Colin Barker_, Sep 12 2018 %e A228681 Some solutions for n=4: %e A228681 ..0..0..0..0..0..0....0..0..0..1..0..0....0..0..0..1..0..0....1..0..1..0..1..0 %e A228681 ..1..0..0..1..0..0....0..1..0..1..0..1....0..0..0..0..0..1....0..0..0..0..0..0 %e A228681 ..0..0..0..0..0..1....0..0..0..0..0..1....1..0..0..0..0..0....1..0..1..0..0..0 %e A228681 ..1..0..0..0..0..0....0..0..0..0..0..1....0..0..1..0..1..0....1..0..0..0..1..0 %Y A228681 Column 6 of A228683. %K A228681 nonn %O A228681 1,1 %A A228681 _R. H. Hardin_, Aug 30 2013