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 A206878 #7 Jul 22 2025 19:45:57 %S A206878 7,49,230,1011,4705,22412,105936,497727,2339729,11013295,51846666, %T A206878 244013222,1148355280,5404522372,25435928407,119711433603, %U A206878 563405871570,2651594982047,12479394172896,58732688555813,276417903263710 %N A206878 Number of nX3 0..1 arrays avoiding 0 1 0 horizontally and 1 0 1 vertically. %C A206878 Column 3 of A206883 %H A206878 R. H. Hardin, <a href="/A206878/b206878.txt">Table of n, a(n) for n = 1..210</a> %F A206878 Empirical: a(n) = 5*a(n-1) -7*a(n-2) +24*a(n-3) +8*a(n-4) +11*a(n-5) +32*a(n-6) -22*a(n-7) -44*a(n-8) +11*a(n-9) +13*a(n-10) -a(n-11) -a(n-12) %e A206878 Some solutions for n=4 %e A206878 ..1..0..1....1..1..1....0..1..1....0..1..1....1..0..0....1..0..0....0..0..1 %e A206878 ..0..0..1....1..1..1....0..0..1....0..0..1....0..0..1....0..0..0....0..0..0 %e A206878 ..0..1..1....0..1..1....0..0..1....1..0..0....0..0..1....0..1..1....1..1..0 %e A206878 ..1..0..0....0..1..1....0..0..1....0..0..0....0..1..1....1..1..0....0..1..1 %K A206878 nonn %O A206878 1,1 %A A206878 _R. H. Hardin_ Feb 13 2012