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 A207886 #7 Jul 22 2025 20:56:01 %S A207886 9,81,177,575,1360,3106,8652,22114,53620,139806,360132,899952,2300016, %T A207886 5898082,14925674,37975776,96993892,246541258,627068300,1598281686, %U A207886 4067781864,10349972204,26357799164,67101532924,170780094962 %N A207886 Number of 4Xn 0..1 arrays avoiding 0 0 0 and 1 0 1 horizontally and 0 1 1 and 1 1 0 vertically. %C A207886 Row 4 of A207885 %H A207886 R. H. Hardin, <a href="/A207886/b207886.txt">Table of n, a(n) for n = 1..210</a> %F A207886 Empirical: a(n) = a(n-1) +a(n-2) +11*a(n-3) -2*a(n-4) -7*a(n-5) -31*a(n-6) +a(n-7) +6*a(n-8) +39*a(n-9) -4*a(n-10) +7*a(n-11) -24*a(n-12) -a(n-13) -6*a(n-14) +6*a(n-15) for n>17 %e A207886 Some solutions for n=4 %e A207886 ..0..0..1..0....1..1..0..0....0..0..1..1....0..0..1..0....1..1..0..0 %e A207886 ..1..0..0..1....1..1..0..0....1..0..0..1....0..0..1..0....0..0..1..0 %e A207886 ..0..0..1..0....1..1..1..0....0..0..1..1....1..1..1..0....0..1..0..0 %e A207886 ..1..0..0..1....1..1..0..0....1..0..0..1....0..0..1..0....1..0..0..1 %K A207886 nonn %O A207886 1,1 %A A207886 _R. H. Hardin_ Feb 21 2012