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 A207501 #7 Jul 22 2025 20:30:45 %S A207501 9,81,297,1004,2942,7305,17911,40262,87990,187012,385400,783726, %T A207501 1564402,3084097,6019187,11629307,22307563,42493220,80468378, %U A207501 151622295,284370183,531240776,988874960,1834816342,3394683936,6264203818,11531988896 %N A207501 Number of 4Xn 0..1 arrays avoiding 0 0 0 and 0 1 1 horizontally and 0 0 1 and 1 0 0 vertically. %C A207501 Row 4 of A207500 %H A207501 R. H. Hardin, <a href="/A207501/b207501.txt">Table of n, a(n) for n = 1..210</a> %F A207501 Empirical: a(n) = 4*a(n-1) -a(n-2) -10*a(n-3) -3*a(n-4) +28*a(n-5) +4*a(n-6) -32*a(n-7) -15*a(n-8) +26*a(n-9) +8*a(n-10) -6*a(n-11) +8*a(n-12) -4*a(n-13) -13*a(n-14) -2*a(n-15) +11*a(n-16) -2*a(n-17) +a(n-18) -2*a(n-21) +a(n-22) %e A207501 Some solutions for n=4 %e A207501 ..1..1..0..1....1..0..1..0....1..1..0..1....1..1..0..1....1..1..1..1 %e A207501 ..0..0..1..0....0..1..0..0....1..1..0..1....0..1..0..0....1..1..1..1 %e A207501 ..1..1..1..1....1..0..1..0....0..1..0..0....1..1..0..1....1..1..1..1 %e A207501 ..1..0..1..0....0..1..0..0....1..0..0..1....0..1..0..1....1..0..1..0 %K A207501 nonn %O A207501 1,1 %A A207501 _R. H. Hardin_ Feb 18 2012