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 A207804 #7 Jul 22 2025 20:51:15 %S A207804 10,100,378,1970,9168,44538,212814,1022652,4904350,23540322,112961952, %T A207804 542115042,2601499810,12484112380,59908695042,287491745166, %U A207804 1379628582160,6620628961338,31771352156610,152465531316540,731656970494958 %N A207804 Number of nX4 0..1 arrays avoiding 0 0 0 and 0 0 1 horizontally and 0 1 0 and 1 0 1 vertically. %C A207804 Column 4 of A207808 %H A207804 R. H. Hardin, <a href="/A207804/b207804.txt">Table of n, a(n) for n = 1..210</a> %F A207804 Empirical: a(n) = 4*a(n-1) +a(n-2) -8*a(n-3) +53*a(n-4) +166*a(n-5) +347*a(n-6) +208*a(n-7) -166*a(n-8) -780*a(n-9) -2484*a(n-10) -3678*a(n-11) -3721*a(n-12) -644*a(n-13) +1359*a(n-14) +1318*a(n-15) +536*a(n-16) -82*a(n-17) +446*a(n-18) -106*a(n-19) -85*a(n-20) -32*a(n-21) -47*a(n-22) +28*a(n-23) -9*a(n-24) +a(n-26) %e A207804 Some solutions for n=4 %e A207804 ..1..0..1..1....1..0..1..0....0..1..1..0....0..1..1..0....1..1..0..0 %e A207804 ..0..1..1..0....1..1..0..1....1..1..0..0....1..1..0..0....1..1..1..0 %e A207804 ..0..1..0..0....0..1..0..1....1..1..0..0....1..1..0..0....0..1..1..1 %e A207804 ..0..1..0..0....0..1..1..1....0..1..1..1....1..1..1..1....0..1..1..1 %K A207804 nonn %O A207804 1,1 %A A207804 _R. H. Hardin_ Feb 20 2012