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 A232957 #8 Oct 06 2018 11:45:41 %S A232957 16,147,1881,22971,283131,3484893,42904365,528197043,6502696923, %T A232957 80055386493,985570487037,12133464037491,149376378762507, %U A232957 1838988638568957,22639986598509837,278723306070050355 %N A232957 Number of 3 X n 0..3 arrays with no element x(i,j) adjacent to value 3-x(i,j) horizontally, diagonally or antidiagonally, and top left element zero. %H A232957 R. H. Hardin, <a href="/A232957/b232957.txt">Table of n, a(n) for n = 1..210</a> %F A232957 Empirical: a(n) = 12*a(n-1) + 7*a(n-2) - 40*a(n-3) + 12*a(n-4). %F A232957 Empirical g.f.: x*(16 - 45*x + 5*x^2 + 10*x^3) / (1 - 12*x - 7*x^2 + 40*x^3 - 12*x^4). - _Colin Barker_, Oct 06 2018 %e A232957 Some solutions for n=4: %e A232957 ..0..0..1..1....0..0..0..0....0..1..0..0....0..1..1..1....0..1..1..1 %e A232957 ..0..1..1..0....1..1..1..1....0..1..1..0....3..1..1..3....0..0..0..1 %e A232957 ..0..0..0..1....1..0..1..0....0..0..1..1....3..1..3..1....1..1..1..0 %Y A232957 Row 3 of A232955. %K A232957 nonn %O A232957 1,1 %A A232957 _R. H. Hardin_, Dec 02 2013