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 A208143 #7 Jul 22 2025 21:11:34 %S A208143 8,64,240,900,2400,6400,14000,30625,58800,112896,197568,345744,564480, %T A208143 921600,1425600,2205225,3267000,4840000,6921200,9897316,13741728, %U A208143 19079424,25836720,34987225,46373600,61465600,79968000,104040000 %N A208143 Number of 4Xn 0..1 arrays avoiding 0 0 1 and 0 1 1 horizontally and 0 0 1 and 1 0 1 vertically. %C A208143 Row 4 of A208142 %H A208143 R. H. Hardin, <a href="/A208143/b208143.txt">Table of n, a(n) for n = 1..210</a> %F A208143 Empirical: a(n) = 2*a(n-1) +6*a(n-2) -14*a(n-3) -14*a(n-4) +42*a(n-5) +14*a(n-6) -70*a(n-7) +70*a(n-9) -14*a(n-10) -42*a(n-11) +14*a(n-12) +14*a(n-13) -6*a(n-14) -2*a(n-15) +a(n-16) %e A208143 Some solutions for n=4 %e A208143 ..0..0..0..0....0..0..0..0....1..1..0..1....1..0..0..0....1..1..1..1 %e A208143 ..1..0..0..0....0..1..0..0....0..0..0..0....0..1..0..0....1..1..1..1 %e A208143 ..0..0..0..0....0..0..0..0....0..0..0..0....0..0..0..0....1..1..1..1 %e A208143 ..0..0..0..0....0..0..0..0....0..0..0..0....0..0..0..0....1..1..1..1 %K A208143 nonn %O A208143 1,1 %A A208143 _R. H. Hardin_ Feb 23 2012