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 A268635 #8 Jan 14 2019 09:01:48 %S A268635 36,504,5178,47640,412740,3440052,27906474,221913216,1737860310, %T A268635 13445785116,103012659468,782824552488,5908380409134,44334271544616, %U A268635 330997648937706,2460394469263680,18218335277707956,134439600276305244 %N A268635 Number of n_X_4 0..2 arrays with some element plus some horizontally or vertically adjacent neighbor totalling two exactly once. %H A268635 R. H. Hardin, <a href="/A268635/b268635.txt">Table of n, a(n) for n = 1..210</a> %F A268635 Empirical: a(n) = 18*a(n-1) - 111*a(n-2) + 282*a(n-3) - 333*a(n-4) + 180*a(n-5) - 36*a(n-6) for n>7. %F A268635 Empirical g.f.: 6*x*(6 - 24*x + 17*x^2 + 38*x^3 - 27*x^4 - 12*x^5 + 8*x^6) / (1 - 9*x + 15*x^2 - 6*x^3)^2. - _Colin Barker_, Jan 14 2019 %e A268635 Some solutions for n=4: %e A268635 ..0..0..1..0. .0..0..1..0. .2..1..2..1. .1..2..2..2. .2..1..0..1 %e A268635 ..0..0..0..1. .2..1..0..1. .2..2..1..0. .0..2..2..1. .2..2..1..0 %e A268635 ..1..0..1..0. .2..2..1..0. .1..1..0..0. .1..2..1..0. .1..2..1..0 %e A268635 ..1..0..0..1. .2..1..2..1. .0..0..1..0. .2..1..2..1. .2..1..0..0 %Y A268635 Column 4 of A268639. %K A268635 nonn %O A268635 1,1 %A A268635 _R. H. Hardin_, Feb 09 2016