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 A207904 #7 Jul 22 2025 20:57:57 %S A207904 9,81,289,841,2209,5041,11025,22801,45369,88209,167281,312481,576081, %T A207904 1050625,1901641,3418801,6115729,10896601,19351201,34281025,60606225, %U A207904 106977649,188595289,332150625,584527329,1028035969,1807185121 %N A207904 Number of nX4 0..1 arrays avoiding 0 0 0 and 0 1 0 horizontally and 0 0 0 and 0 1 1 vertically. %C A207904 Column 4 of A207908 %H A207904 R. H. Hardin, <a href="/A207904/b207904.txt">Table of n, a(n) for n = 1..210</a> %F A207904 Empirical: a(n) = 4*a(n-1) -3*a(n-2) -4*a(n-3) -a(n-4) +14*a(n-5) -6*a(n-6) -5*a(n-7) -3*a(n-8) +7*a(n-9) -4*a(n-10) +3*a(n-11) -2*a(n-14) +a(n-15) %e A207904 Some solutions for n=4 %e A207904 ..0..1..1..1....1..0..0..1....1..1..0..0....0..1..1..0....1..0..1..1 %e A207904 ..0..1..1..1....0..0..1..1....1..1..1..0....1..0..1..1....0..0..1..1 %e A207904 ..1..1..1..1....1..1..0..1....1..0..0..1....0..1..1..0....0..1..1..1 %e A207904 ..0..1..1..1....0..0..1..1....0..1..1..0....1..0..1..1....1..0..0..1 %K A207904 nonn %O A207904 1,1 %A A207904 _R. H. Hardin_ Feb 21 2012