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 A276293 #8 Feb 05 2019 07:53:34 %S A276293 1,4,11,31,88,250,710,2016,5724,16252,46144,131016,371992,1056192, %T A276293 2998832,8514544,24175232,68640416,194889824,553348096,1571113920, %U A276293 4460842944,12665612288,35961305216,102104457600,289903834112 %N A276293 Number of n X 2 0..2 arrays with no element equal to any value at offset (-2,-1) (-1,1) or (0,-1) and new values introduced in order 0..2. %H A276293 R. H. Hardin, <a href="/A276293/b276293.txt">Table of n, a(n) for n = 1..210</a> %F A276293 Empirical: a(n) = 4*a(n-1) - 4*a(n-2) + 2*a(n-3) for n>4. %F A276293 Empirical g.f.: x*(1 - x^2 + x^3) / (1 - 4*x + 4*x^2 - 2*x^3). - _Colin Barker_, Feb 05 2019 %e A276293 Some solutions for n=4: %e A276293 ..0..1. .0..1. .0..1. .0..1. .0..1. .0..1. .0..1. .0..1. .0..1. .0..1 %e A276293 ..0..2. .2..1. .0..1. .0..2. .2..0. .0..2. .0..1. .0..1. .0..1. .2..1 %e A276293 ..0..1. .2..1. .0..2. .0..1. .1..2. .0..2. .2..1. .0..2. .0..1. .2..1 %e A276293 ..0..2. .0..1. .0..1. .0..1. .0..1. .0..2. .2..1. .1..2. .0..2. .2..1 %Y A276293 Column 2 of A276299. %K A276293 nonn %O A276293 1,2 %A A276293 _R. H. Hardin_, Aug 28 2016