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 A181219 #5 Jul 22 2025 08:36:34 %S A181219 7,49,230,1209,6475,34020,179097,944514,4978956,26241679,138316703, %T A181219 729070278,3842881010,20255521442,106765644778,562755120940, %U A181219 2966245831625,15634892911279,82410528967137,434380653636920 %N A181219 Number of nX3 binary matrices with no three 1's adjacent in a line horizontally, vertically, diagonally or antidiagonally. %C A181219 Column 3 of A181224 %H A181219 R. H. Hardin, <a href="/A181219/b181219.txt">Table of n, a(n) for n=1..350</a> %F A181219 Empirical: a(n)=2*a(n-1)+8*a(n-2)+38*a(n-3)+51*a(n-4)+41*a(n-5)-48*a(n-6)-88*a(n-7)-4*a(n-8)-8*a(n-9)-15*a(n-10)+14*a(n-11)-7*a(n-12)+a(n-13)-2*a(n-14) %e A181219 Some avoided solutions for 4X3 %e A181219 ..1..0..0....1..1..0....1..0..0....1..0..0....0..0..1....0..0..0....0..0..1 %e A181219 ..0..1..0....0..1..0....0..0..1....0..1..0....0..1..0....0..0..0....0..1..0 %e A181219 ..0..0..1....0..0..1....0..1..0....0..0..1....1..0..1....0..0..1....1..0..0 %e A181219 ..0..1..0....0..0..0....1..0..0....1..0..0....0..0..0....1..1..1....0..0..1 %K A181219 nonn %O A181219 1,1 %A A181219 _R. H. Hardin_ Oct 10 2010