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 A208684 #7 Jul 22 2025 21:27:28 %S A208684 10,100,282,927,3430,11067,34627,111642,356116,1121500,3542847, %T A208684 11196360,35283685,111150345,350234962,1103073000,3473204686, %U A208684 10936009567,34431544350,108396961047,341246282767,1074267088938,3381794658280 %N A208684 Number of nX4 0..1 arrays avoiding 0 0 0 and 0 0 1 horizontally and 0 1 1 and 1 0 1 vertically. %C A208684 Column 4 of A208688 %H A208684 R. H. Hardin, <a href="/A208684/b208684.txt">Table of n, a(n) for n = 1..210</a> %F A208684 Empirical: a(n) = 4*a(n-1) -3*a(n-2) +10*a(n-3) -27*a(n-4) -6*a(n-5) -15*a(n-6) +51*a(n-7) +41*a(n-8) +31*a(n-9) -51*a(n-10) -29*a(n-11) -27*a(n-12) +15*a(n-13) +6*a(n-14) +3*a(n-15) -4*a(n-16) +a(n-17) +a(n-19) %e A208684 Some solutions for n=4 %e A208684 ..0..1..1..0....1..0..1..0....0..1..1..0....1..1..0..0....1..1..0..1 %e A208684 ..0..1..1..0....1..1..1..0....1..1..0..1....0..1..0..1....1..1..0..1 %e A208684 ..1..1..0..1....1..0..1..1....0..1..0..0....0..1..0..0....0..1..1..0 %e A208684 ..0..1..0..0....1..0..1..0....0..1..0..0....1..0..1..0....0..1..0..0 %K A208684 nonn %O A208684 1,1 %A A208684 _R. H. Hardin_ Mar 01 2012