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 A207489 #7 Jul 22 2025 20:29:40 %S A207489 9,81,177,530,1322,2749,6217,12712,25908,52474,103704,205390,402848, %T A207489 787367,1536289,2987863,5806685,11270614,21859130,42378217,82121061, %U A207489 159101032,308184196,596883878,1155938528,2238468542,4334604962 %N A207489 Number of 4Xn 0..1 arrays avoiding 0 0 0 and 0 1 1 horizontally and 0 1 1 and 1 1 0 vertically. %C A207489 Row 4 of A207488 %H A207489 R. H. Hardin, <a href="/A207489/b207489.txt">Table of n, a(n) for n = 1..210</a> %F A207489 Empirical: a(n) = 2*a(n-1) +2*a(n-2) +a(n-3) -11*a(n-4) -5*a(n-5) +a(n-6) +23*a(n-7) +14*a(n-8) +4*a(n-9) -37*a(n-10) -31*a(n-11) -6*a(n-12) +43*a(n-13) +31*a(n-14) +2*a(n-15) -28*a(n-16) -15*a(n-17) +9*a(n-19) +3*a(n-20) -a(n-22) %e A207489 Some solutions for n=4 %e A207489 ..1..1..0..0....0..0..1..0....1..1..0..1....0..1..0..0....1..1..0..1 %e A207489 ..0..1..0..1....1..0..1..0....0..0..1..0....0..1..0..1....1..1..0..1 %e A207489 ..1..1..0..0....0..0..1..0....0..1..0..1....0..1..0..0....1..1..1..1 %e A207489 ..0..1..0..1....0..0..1..0....1..0..1..0....1..1..1..1....1..1..0..1 %K A207489 nonn %O A207489 1,1 %A A207489 _R. H. Hardin_ Feb 18 2012