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 A207956 #7 Jul 22 2025 21:03:06 %S A207956 9,81,281,989,3923,15921,67007,286299,1240603,5420023,23828357, %T A207956 105188575,465711669,2065999789,9177987717,40811215453,181593070243, %U A207956 808383490865,3599754765767,16033313059243,71423194026691,318200352273815 %N A207956 Number of nX4 0..1 arrays avoiding 0 0 0 and 1 0 1 horizontally and 0 0 1 and 1 0 0 vertically. %C A207956 Column 4 of A207960 %H A207956 R. H. Hardin, <a href="/A207956/b207956.txt">Table of n, a(n) for n = 1..210</a> %F A207956 Empirical: a(n) = 7*a(n-1) +2*a(n-2) -87*a(n-3) +48*a(n-4) +445*a(n-5) -280*a(n-6) -1175*a(n-7) +613*a(n-8) +1664*a(n-9) -614*a(n-10) -1206*a(n-11) +264*a(n-12) +392*a(n-13) -32*a(n-14) -40*a(n-15) for n>16 %e A207956 Some solutions for n=4 %e A207956 ..0..1..1..0....1..0..0..1....1..1..0..0....0..1..0..0....0..0..1..1 %e A207956 ..0..0..1..1....0..1..0..0....0..0..1..0....0..1..1..1....0..1..1..0 %e A207956 ..0..1..0..0....1..0..0..1....1..1..0..0....0..1..1..1....0..1..1..1 %e A207956 ..0..0..1..1....0..1..0..0....0..1..1..0....0..1..1..1....0..0..1..1 %K A207956 nonn %O A207956 1,1 %A A207956 _R. H. Hardin_ Feb 21 2012