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 A206780 #7 Jul 22 2025 19:40:34 %S A206780 7,49,230,1020,4120,16109,61003,227197,834806,3041436,11009856, %T A206780 39680145,142545383,510891025,1827957230,6532356532,23322885552, %U A206780 83216416445,296774223739,1058010185133,3770863749966,13437211488900,47875876583016 %N A206780 Number of nX3 0..1 arrays avoiding 0 0 1 horizontally and 0 1 1 vertically. %C A206780 Column 3 of A206785 %H A206780 R. H. Hardin, <a href="/A206780/b206780.txt">Table of n, a(n) for n = 1..210</a> %F A206780 Empirical: a(n) = 7*a(n-1) -10*a(n-2) -23*a(n-3) +57*a(n-4) +6*a(n-5) -75*a(n-6) +21*a(n-7) +34*a(n-8) -13*a(n-9) -5*a(n-10) +2*a(n-11) %e A206780 Some solutions for n=4 %e A206780 ..1..1..0....0..1..1....0..0..0....1..1..1....0..1..0....1..1..0....0..1..1 %e A206780 ..1..0..1....1..1..0....0..1..1....1..1..0....1..0..1....0..0..0....0..1..1 %e A206780 ..1..0..0....0..1..1....1..0..0....1..0..1....0..0..0....1..1..1....0..1..1 %e A206780 ..0..1..1....1..0..0....0..0..0....1..1..0....1..1..0....0..0..0....0..1..1 %K A206780 nonn %O A206780 1,1 %A A206780 _R. H. Hardin_ Feb 12 2012