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 A207070 #7 Jul 22 2025 19:59:47 %S A207070 6,36,102,288,896,2499,6634,17848,47192,122200,315315,809784,2063670, %T A207070 5238225,13261490,33465000,84237826,211676500,531027000,1330245423, %U A207070 3328592562,8320844952,20782671568,51871277456,129387019195,322571437760 %N A207070 Number of 3Xn 0..1 arrays avoiding 0 0 1 and 0 1 0 horizontally and 0 0 1 and 1 0 1 vertically. %C A207070 Row 3 of A207068 %H A207070 R. H. Hardin, <a href="/A207070/b207070.txt">Table of n, a(n) for n = 1..210</a> %F A207070 Empirical: a(n) = 5*a(n-1) -9*a(n-2) +21*a(n-3) -56*a(n-4) +64*a(n-5) -89*a(n-6) +192*a(n-7) -119*a(n-8) +117*a(n-9) -305*a(n-10) +46*a(n-11) -64*a(n-12) +323*a(n-13) +39*a(n-14) +36*a(n-15) -228*a(n-16) -56*a(n-17) -4*a(n-18) +80*a(n-19) +24*a(n-20) -16*a(n-22) %e A207070 Some solutions for n=4 %e A207070 ..0..0..0..0....0..0..0..0....0..1..1..0....1..1..0..0....1..0..0..0 %e A207070 ..0..1..1..1....1..1..1..0....0..1..1..1....0..0..0..0....0..1..1..1 %e A207070 ..0..1..1..0....1..1..1..0....0..1..1..0....0..0..0..0....0..1..1..0 %K A207070 nonn %O A207070 1,1 %A A207070 _R. H. Hardin_ Feb 14 2012