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 A303520 #4 Apr 25 2018 12:37:35 %S A303520 3,11,18,39,95,246,687,2023,6126,19571,63599,209618,700539,2356511, %T A303520 7961506,26985119,91629471,311488830,1059693975,3606749879, %U A303520 12279357318,41813315995,142397488591,484976347386,1651802107971,5626099528751 %N A303520 Number of nX3 0..1 arrays with every element equal to 0, 1, 3, 4, 5 or 6 horizontally, diagonally or antidiagonally adjacent elements, with upper left element zero. %C A303520 Column 3 of A303525. %H A303520 R. H. Hardin, <a href="/A303520/b303520.txt">Table of n, a(n) for n = 1..210</a> %F A303520 Empirical: a(n) = 4*a(n-1) -3*a(n-2) +10*a(n-3) -22*a(n-4) +6*a(n-5) -31*a(n-6) +10*a(n-7) -3*a(n-8) -14*a(n-9) -8*a(n-10) -32*a(n-11) -16*a(n-12) for n>15 %e A303520 Some solutions for n=5 %e A303520 ..0..0..0. .0..1..1. .0..1..0. .0..1..0. .0..1..0. .0..0..1. .0..1..0 %e A303520 ..0..1..0. .0..0..0. .1..1..0. .0..1..1. .0..1..1. .1..1..1. .0..0..0 %e A303520 ..0..1..1. .0..1..0. .0..1..0. .0..1..0. .0..1..0. .1..0..1. .0..1..0 %e A303520 ..0..1..0. .0..1..0. .0..1..0. .0..1..0. .0..0..0. .1..0..1. .0..1..0 %e A303520 ..0..0..0. .0..0..0. .1..0..0. .0..0..0. .0..1..0. .0..1..1. .0..0..0 %Y A303520 Cf. A303525. %K A303520 nonn %O A303520 1,1 %A A303520 _R. H. Hardin_, Apr 25 2018