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 A275184 #8 Feb 01 2019 05:32:27 %S A275184 4,12,41,141,482,1651,5653,19356,66277,226937,777050,2660679,9110369, %T A275184 31194604,106812721,365734965,1252304626,4287987275,14682397949, %U A275184 50273658876,172140871373,589423572097,2018231606314,6910580115135 %N A275184 Number of 4 X n 0..2 arrays with no element equal to any value at offset (-2,-1) (-1,0) or (-1,1) and new values introduced in order 0..2. %H A275184 R. H. Hardin, <a href="/A275184/b275184.txt">Table of n, a(n) for n = 1..210</a> %F A275184 Empirical: a(n) = 2*a(n-1) + 4*a(n-2) + 3*a(n-3) for n>4. %F A275184 Empirical g.f.: x*(4 + 4*x + x^2 - x^3) / (1 - 2*x - 4*x^2 - 3*x^3). - _Colin Barker_, Feb 01 2019 %e A275184 Some solutions for n=4: %e A275184 ..0..1..2..2. .0..1..2..0. .0..0..1..1. .0..0..1..1. .0..1..1..2 %e A275184 ..2..0..0..1. .2..0..1..1. .2..2..2..0. .2..2..0..0. .2..0..0..0 %e A275184 ..1..2..2..0. .1..2..2..0. .1..1..1..2. .0..1..1..2. .1..2..2..2 %e A275184 ..0..1..1..2. .0..0..1..2. .0..0..0..1. .2..0..0..1. .0..0..1..1 %Y A275184 Row 4 of A275183. %K A275184 nonn %O A275184 1,1 %A A275184 _R. H. Hardin_, Jul 19 2016