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 A208685 #7 Jul 22 2025 21:27:34 %S A208685 16,256,768,2889,12096,41013,133207,444912,1448128,4616800,14733663, %T A208685 46884096,148366461,468807885,1480447408,4669224000,14715790096, %U A208685 46366826149,146050380000,459933577353,1448231824455,4559797881648 %N A208685 Number of nX5 0..1 arrays avoiding 0 0 0 and 0 0 1 horizontally and 0 1 1 and 1 0 1 vertically. %C A208685 Column 5 of A208688 %H A208685 R. H. Hardin, <a href="/A208685/b208685.txt">Table of n, a(n) for n = 1..210</a> %F A208685 Empirical: a(n) = 4*a(n-1) -3*a(n-2) +10*a(n-3) -27*a(n-4) -6*a(n-5) -15*a(n-6) +51*a(n-7) +41*a(n-8) +31*a(n-9) -51*a(n-10) -29*a(n-11) -27*a(n-12) +15*a(n-13) +6*a(n-14) +3*a(n-15) -4*a(n-16) +a(n-17) +a(n-19) %e A208685 Some solutions for n=4 %e A208685 ..0..1..1..1..1....0..1..1..1..1....0..1..0..1..1....1..1..0..1..1 %e A208685 ..0..1..0..1..0....1..1..1..1..0....1..1..1..1..1....1..1..1..1..0 %e A208685 ..1..1..0..1..0....0..1..0..1..0....0..1..0..1..0....0..1..0..1..0 %e A208685 ..0..1..0..1..0....0..1..0..1..0....0..1..0..1..0....0..1..0..1..1 %K A208685 nonn %O A208685 1,1 %A A208685 _R. H. Hardin_ Mar 01 2012