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 A297577 #8 Mar 01 2019 06:20:52 %S A297577 3,11,36,102,370,1243,3854,13078,43861,141109,468638,1561065,5101698, %T A297577 16842125,55830567,183595621,605376713,2001499842,6596762626, %U A297577 21752445702,71828204711,236917416288,781388833534,2578812375049,8507768092491 %N A297577 Number of n X 3 0..1 arrays with every 1 horizontally, diagonally or antidiagonally adjacent to 1 or 4 neighboring 1s. %H A297577 R. H. Hardin, <a href="/A297577/b297577.txt">Table of n, a(n) for n = 1..210</a> %F A297577 Empirical: a(n) = a(n-1) + 2*a(n-2) + 19*a(n-3) + 4*a(n-4) - 17*a(n-5) - 8*a(n-6). %F A297577 Empirical g.f.: x*(3 + 8*x + 19*x^2 - 13*x^3 - 25*x^4 - 8*x^5) / ((1 - x)*(1 - 2*x^2 - 21*x^3 - 25*x^4 - 8*x^5)). - _Colin Barker_, Mar 01 2019 %e A297577 Some solutions for n=7: %e A297577 ..0..0..0. .1..0..1. .0..0..0. .0..0..0. .0..0..0. .1..1..0. .0..0..0 %e A297577 ..0..1..1. .1..1..1. .0..1..1. .1..0..1. .1..0..0. .0..0..0. .0..0..0 %e A297577 ..0..0..0. .0..0..0. .0..0..0. .0..1..1. .1..1..0. .1..0..1. .0..1..1 %e A297577 ..1..0..1. .0..1..0. .0..0..1. .0..0..1. .1..0..1. .1..1..1. .0..0..0 %e A297577 ..1..1..1. .1..0..0. .1..1..1. .0..0..0. .1..0..1. .0..0..0. .1..0..1 %e A297577 ..0..0..0. .1..0..1. .0..0..1. .0..1..0. .1..1..0. .0..0..1. .0..1..1 %e A297577 ..0..1..1. .1..1..1. .0..0..0. .0..0..1. .1..0..0. .0..1..0. .0..0..1 %Y A297577 Column 3 of A297582. %K A297577 nonn %O A297577 1,1 %A A297577 _R. H. Hardin_, Jan 01 2018