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 A207897 #7 Jul 22 2025 20:57:10 %S A207897 10,100,292,870,2446,6952,20168,57838,164914,473632,1360740,3896086, %T A207897 11165294,32038792,91859552,263284722,754983634,2164966616,6206791972, %U A207897 17795617610,51026354878,146302277604,419468202104,1202710746958 %N A207897 Number of 4Xn 0..1 arrays avoiding 0 0 0 and 1 0 1 horizontally and 0 0 0 and 1 1 1 vertically. %C A207897 Row 4 of A207895 %H A207897 R. H. Hardin, <a href="/A207897/b207897.txt">Table of n, a(n) for n = 1..210</a> %F A207897 Empirical: a(n) = 3*a(n-2) +10*a(n-3) +18*a(n-4) -2*a(n-5) -22*a(n-6) -7*a(n-7) -12*a(n-9) -8*a(n-10) -6*a(n-11) -6*a(n-12) -3*a(n-13) -a(n-14) +3*a(n-15) +a(n-16) -a(n-17) for n>18 %e A207897 Some solutions for n=4 %e A207897 ..1..0..0..1....0..1..1..0....1..0..0..1....1..1..0..0....0..1..1..0 %e A207897 ..1..1..0..0....0..1..1..1....0..1..1..0....0..0..1..1....1..1..0..0 %e A207897 ..0..1..1..0....1..0..0..1....1..0..0..1....1..1..0..0....0..0..1..1 %e A207897 ..0..0..1..1....1..1..1..0....1..1..1..1....1..0..0..1....1..1..1..0 %K A207897 nonn %O A207897 1,1 %A A207897 _R. H. Hardin_ Feb 21 2012