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 A207748 #7 Jul 24 2025 19:38:28 %S A207748 9,81,289,900,3249,11449,42436,157609,597529,2280100,8791225,34093921, %T A207748 133033156,521345889,2051093521,8093881156,32021313025,126943276681, %U A207748 504097160004,2004526450969,7979839669321,31795772223076,126783929266569 %N A207748 Number of nX4 0..1 arrays avoiding 0 0 1 and 0 1 1 horizontally and 0 0 1 and 1 0 0 vertically. %C A207748 Column 4 of A207752 %H A207748 R. H. Hardin, <a href="/A207748/b207748.txt">Table of n, a(n) for n = 1..210</a> %F A207748 Empirical: a(n) = 9*a(n-1) -15*a(n-2) -70*a(n-3) +208*a(n-4) +148*a(n-5) -795*a(n-6) +15*a(n-7) +1267*a(n-8) -318*a(n-9) -840*a(n-10) +280*a(n-11) +176*a(n-12) -64*a(n-13) for n>14 %e A207748 Some solutions for n=4 %e A207748 ..1..1..1..1....1..0..0..0....0..1..0..0....1..0..0..0....0..1..0..0 %e A207748 ..0..0..0..0....1..1..0..1....0..1..0..1....0..1..0..0....0..0..0..0 %e A207748 ..1..1..1..1....0..1..0..0....0..0..0..0....1..0..0..0....0..1..0..0 %e A207748 ..0..0..0..0....1..1..0..1....0..1..0..1....1..1..0..0....0..0..0..0 %K A207748 nonn %O A207748 1,1 %A A207748 _R. H. Hardin_ Feb 19 2012