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 A297309 #7 Feb 26 2019 12:06:09 %S A297309 4,23,117,609,3159,16389,85041,441225,2289339,11878281,61631001, %T A297309 319774761,1659164103,8608637997,44666257401,231752633913, %U A297309 1202457662523,6238998904833,32371291359585,167959719216009,871465613342823 %N A297309 Number of n X 3 0..1 arrays with every 1 horizontally or antidiagonally adjacent to 1 or 2 neighboring 1s. %H A297309 R. H. Hardin, <a href="/A297309/b297309.txt">Table of n, a(n) for n = 1..210</a> %F A297309 Empirical: a(n) = 3*a(n-1) + 11*a(n-2) + 3*a(n-3) - 6*a(n-4). %F A297309 Empirical g.f.: x*(4 + 11*x + 4*x^2 - 7*x^3) / (1 - 3*x - 11*x^2 - 3*x^3 + 6*x^4). - _Colin Barker_, Feb 26 2019 %e A297309 Some solutions for n=5: %e A297309 ..1..1..1. .0..1..0. .1..1..0. .0..1..0. .1..1..0. .0..0..0. .1..1..0 %e A297309 ..0..1..0. .1..0..0. .1..1..1. .1..0..1. .1..1..0. .0..0..0. .1..1..1 %e A297309 ..1..0..0. .1..1..1. .0..0..0. .0..1..0. .1..0..1. .0..0..0. .0..0..0 %e A297309 ..0..0..1. .0..1..0. .1..1..1. .1..1..0. .0..1..0. .1..1..0. .0..1..0 %e A297309 ..1..1..0. .0..1..1. .0..1..1. .0..0..0. .0..1..1. .1..1..1. .1..1..1 %Y A297309 Column 3 of A297314. %K A297309 nonn %O A297309 1,1 %A A297309 _R. H. Hardin_, Dec 28 2017