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 A199650 #7 Jul 22 2025 13:21:43 %S A199650 5,113,2584,59212,1357484,31120632,713445976,16355879648,374961537040, %T A199650 8596061907680,197066293538400,4517780870646656,103570953858672192, %U A199650 2374383085485820032,54433167085958461312,1247890324488906825728 %N A199650 Number of nX3 0..2 arrays with values 0..2 introduced in row major order and each element equal to no more than two horizontal and vertical neighbors. %C A199650 Column 3 of A199655 %H A199650 R. H. Hardin, <a href="/A199650/b199650.txt">Table of n, a(n) for n = 1..200</a> %F A199650 Empirical: a(n) = 21*a(n-1) +44*a(n-2) +8*a(n-3) -96*a(n-4) -364*a(n-5) -264*a(n-6) +256*a(n-7) +288*a(n-8) +64*a(n-9) for n>10 %e A199650 Some solutions for n=4 %e A199650 ..0..0..1....0..0..1....0..1..1....0..1..0....0..0..1....0..0..1....0..1..2 %e A199650 ..1..0..1....1..0..2....0..2..2....1..0..1....1..1..1....2..2..0....1..0..1 %e A199650 ..0..2..2....1..2..0....1..0..0....0..0..2....1..0..2....2..1..0....1..1..0 %e A199650 ..1..2..2....0..0..2....2..2..2....2..2..0....1..0..0....2..0..0....0..0..2 %K A199650 nonn %O A199650 1,1 %A A199650 _R. H. Hardin_ Nov 08 2011