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 A207875 #7 Jul 22 2025 20:54:34 %S A207875 9,81,164,400,824,1940,4200,9276,21004,46026,102674,228630,506868, %T A207875 1128070,2505156,5569740,12380188,27502690,61145106,135886522, %U A207875 301975112,671190932,1491685306,3315241202,7368059728,16375432824,36394465410 %N A207875 Number of nX4 0..1 arrays avoiding 0 0 0 and 1 0 1 horizontally and 0 1 0 and 1 1 1 vertically. %C A207875 Column 4 of A207879 %H A207875 R. H. Hardin, <a href="/A207875/b207875.txt">Table of n, a(n) for n = 1..210</a> %F A207875 Empirical: a(n) = 2*a(n-2) +7*a(n-3) +4*a(n-4) -3*a(n-5) -17*a(n-6) -5*a(n-7) +7*a(n-8) +2*a(n-9) -13*a(n-10) -a(n-11) -2*a(n-12) for n>14 %e A207875 Some solutions for n=4 %e A207875 ..0..1..1..1....0..1..0..0....1..1..0..0....1..0..0..1....0..1..1..0 %e A207875 ..1..0..0..1....1..1..0..0....0..0..1..0....0..1..1..1....1..0..0..1 %e A207875 ..1..1..1..0....1..0..0..1....0..1..1..0....0..1..1..0....1..1..1..1 %e A207875 ..0..1..1..0....0..0..1..1....1..1..0..0....1..0..0..1....0..1..1..0 %K A207875 nonn %O A207875 1,1 %A A207875 _R. H. Hardin_ Feb 21 2012