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 A269277 #8 Jan 21 2019 06:22:48 %S A269277 0,108,1368,13896,127512,1104264,9211608,74853576,596581272, %T A269277 4684312584,36347893848,279339197256,2129701963032,16128206816904, %U A269277 121439499248088,909870855444936,6787656513072792,50443519266217224,373614100586474328 %N A269277 Number of 2 X n 0..3 arrays with some element plus some horizontally or antidiagonally adjacent neighbor totalling three exactly once. %H A269277 R. H. Hardin, <a href="/A269277/b269277.txt">Table of n, a(n) for n = 1..210</a> %F A269277 Empirical: a(n) = 14*a(n-1) - 49*a(n-2) for n>4. %F A269277 Conjectures from _Colin Barker_, Jan 21 2019: (Start) %F A269277 G.f.: 36*x^2*(3 - x)*(1 - x) / (1 - 7*x)^2. %F A269277 a(n) = 72 * 7^(n-4) * (60*n-47) for n>2. %F A269277 (End) %e A269277 Some solutions for n=4: %e A269277 ..0..0..2..2. .3..3..1..0. .1..2..2..0. .2..0..2..2. .2..2..2..3 %e A269277 ..0..3..2..3. .1..1..3..2. .2..0..2..2. .1..2..0..0. .1..0..1..1 %Y A269277 Row 2 of A269276. %K A269277 nonn %O A269277 1,2 %A A269277 _R. H. Hardin_, Feb 21 2016