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 A302000 #4 Mar 30 2018 12:30:42 %S A302000 0,5,5,26,84,309,1108,3979,14314,51440,185083,665473,2393298,8606453, %T A302000 30950505,111303112,400265922,1439423515,5176415456,18615274437, %U A302000 66943726862,240741120250,865746384343,3113372499381,11196221683404 %N A302000 Number of 3Xn 0..1 arrays with every element equal to 1, 2 or 4 horizontally or antidiagonally adjacent elements, with upper left element zero. %C A302000 Row 3 of A301999. %H A302000 R. H. Hardin, <a href="/A302000/b302000.txt">Table of n, a(n) for n = 1..210</a> %F A302000 Empirical: a(n) = 2*a(n-1) +6*a(n-2) -2*a(n-4) +2*a(n-5) -9*a(n-6) -50*a(n-7) -37*a(n-8) +34*a(n-9) +43*a(n-10) -16*a(n-11) +15*a(n-12) +18*a(n-13) -7*a(n-14) -2*a(n-16) +4*a(n-17) -6*a(n-18) +a(n-20) %e A302000 Some solutions for n=5 %e A302000 ..0..0..1..1..1. .0..0..0..1..1. .0..0..1..1..1. .0..0..0..1..1 %e A302000 ..0..0..0..0..1. .1..1..1..0..1. .0..1..0..0..0. .1..1..0..1..1 %e A302000 ..1..1..0..1..1. .0..0..0..1..1. .1..1..1..1..1. .1..0..0..1..1 %Y A302000 Cf. A301999. %K A302000 nonn %O A302000 1,2 %A A302000 _R. H. Hardin_, Mar 30 2018