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 A207841 #7 Jul 22 2025 20:52:28 %S A207841 10,100,180,780,2816,9672,35952,130152,462660,1691356,6097536, %T A207841 21894544,79589224,286756120,1033424532,3745763500,13500573120, %U A207841 48729856032,176324800080,635878928776,2296600176396,8301910089028,29954416843008 %N A207841 Number of nX4 0..1 arrays avoiding 0 0 0 and 0 0 1 horizontally and 0 0 0 and 1 1 1 vertically. %C A207841 Column 4 of A207845 %H A207841 R. H. Hardin, <a href="/A207841/b207841.txt">Table of n, a(n) for n = 1..210</a> %F A207841 Empirical: a(n) = 3*a(n-2) +36*a(n-3) +6*a(n-4) +2*a(n-5) -84*a(n-6) +34*a(n-7) +89*a(n-8) -260*a(n-9) +91*a(n-10) -42*a(n-11) +84*a(n-12) -2*a(n-13) +8*a(n-14) +36*a(n-15) +3*a(n-16) +a(n-18) for n>20 %e A207841 Some solutions for n=4 %e A207841 ..0..1..1..0....0..1..1..0....0..1..0..1....0..1..1..1....0..1..0..1 %e A207841 ..0..1..0..1....0..1..0..1....0..1..1..0....1..0..1..0....1..0..1..1 %e A207841 ..1..0..1..0....1..0..1..1....1..0..1..1....0..1..0..1....1..0..1..0 %e A207841 ..1..1..0..1....1..1..1..0....0..1..0..0....1..0..1..1....0..1..0..1 %K A207841 nonn %O A207841 1,1 %A A207841 _R. H. Hardin_ Feb 21 2012