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 A240651 #6 Jul 23 2025 11:05:15 %S A240651 1,2,9,17,43,136,402,1180,3518,10525,31454,94059,281484,842574, %T A240651 2522415,7552239,22613578,67714627,202772197,607215863,1818375168, %U A240651 5445371326,16306993036,48833947510,146241553581,437945846008,1311506541151 %N A240651 Number of nX3 0..1 arrays with no element equal to exactly one horizontal or vertical neighbor, with new values 0..1 introduced in row major order. %C A240651 Column 3 of A240656 %H A240651 R. H. Hardin, <a href="/A240651/b240651.txt">Table of n, a(n) for n = 1..210</a> %F A240651 Empirical: a(n) = 3*a(n-1) +a(n-2) +2*a(n-3) -11*a(n-4) -12*a(n-5) -9*a(n-6) +15*a(n-7) +23*a(n-8) +20*a(n-9) -6*a(n-10) -15*a(n-11) -12*a(n-12) -2*a(n-13) +3*a(n-14) +a(n-15) %e A240651 Some solutions for n=4 %e A240651 ..0..0..0....0..1..0....0..0..0....0..0..0....0..0..1....0..0..0....0..0..1 %e A240651 ..0..0..0....1..0..1....0..1..0....0..0..0....0..0..0....0..0..0....0..0..0 %e A240651 ..0..0..0....0..1..0....0..0..0....0..0..0....0..0..0....0..0..0....0..0..0 %e A240651 ..0..0..0....1..0..1....0..0..1....1..0..0....0..0..1....0..0..1....1..0..0 %K A240651 nonn %O A240651 1,2 %A A240651 _R. H. Hardin_, Apr 09 2014