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 A207565 #7 Jul 22 2025 20:35:31 %S A207565 9,81,221,636,2234,6315,16812,47596,129150,337186,892181,2343529, %T A207565 6046508,15601217,40205083,102833093,262404045,669166152,1701139222, %U A207565 4316129307,10943611348,27709283328,70072708774,177098593806,447280003769 %N A207565 Number of 4Xn 0..1 arrays avoiding 0 0 1 and 0 1 0 horizontally and 0 1 1 and 1 1 0 vertically. %C A207565 Row 4 of A207564 %H A207565 R. H. Hardin, <a href="/A207565/b207565.txt">Table of n, a(n) for n = 1..210</a> %F A207565 Empirical: a(n) = 4*a(n-1) -4*a(n-2) +10*a(n-3) -30*a(n-4) +10*a(n-5) -4*a(n-6) +54*a(n-7) +10*a(n-8) -22*a(n-9) -62*a(n-10) -10*a(n-11) +18*a(n-12) +32*a(n-13) +7*a(n-14) -6*a(n-15) -6*a(n-16) %e A207565 Some solutions for n=4 %e A207565 ..0..0..0..0....1..0..1..1....1..1..0..1....1..0..0..0....0..0..0..0 %e A207565 ..1..0..1..1....0..0..0..0....1..0..1..1....0..1..1..0....1..0..0..0 %e A207565 ..0..0..0..0....1..0..1..1....1..1..0..1....1..0..0..0....0..1..1..0 %e A207565 ..0..1..1..0....0..0..0..0....1..0..1..1....0..0..0..0....1..0..0..0 %K A207565 nonn %O A207565 1,1 %A A207565 _R. H. Hardin_ Feb 18 2012