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 A200796 #7 Jul 22 2025 15:56:19 %S A200796 5,178,9880,583813,34679839,2060918000,122478253815,7278777317468, %T A200796 432571571252989,25707362563355693,1527766813187552208, %U A200796 90793889493222901029,5395804057415427972197,320668071260622898796015 %N A200796 Number of nX3 0..3 arrays with values 0..3 introduced in row major order and each element equal to no more than two horizontal and vertical neighbors. %C A200796 Column 3 of A200801 %H A200796 R. H. Hardin, <a href="/A200796/b200796.txt">Table of n, a(n) for n = 1..200</a> %F A200796 Empirical: a(n) = 60*a(n-1) -17*a(n-2) -964*a(n-3) -2509*a(n-4) +968*a(n-5) +23125*a(n-6) +31652*a(n-7) -4566*a(n-8) -17118*a(n-9) -29646*a(n-10) -74826*a(n-11) -64125*a(n-12) -13932*a(n-13) +4131*a(n-14) +1458*a(n-15) for n>16 %e A200796 Some solutions for n=4 %e A200796 ..0..0..0....0..0..1....0..0..0....0..0..1....0..0..1....0..0..0....0..0..1 %e A200796 ..1..2..2....0..2..2....1..2..2....2..0..1....1..2..0....1..2..0....1..2..0 %e A200796 ..0..0..3....1..2..3....1..2..2....2..3..3....3..0..0....3..1..1....1..3..3 %e A200796 ..2..3..2....0..0..0....2..0..1....3..3..2....3..0..1....0..3..2....3..2..0 %K A200796 nonn %O A200796 1,1 %A A200796 _R. H. Hardin_ Nov 22 2011