cp's OEIS Frontend

A208866 Number of n X 2 0..3 arrays with new values 0..3 introduced in row major order and no element equal to more than one of its immediate leftward or upward or right-upward antidiagonal neighbors.

%I A208866 #9 Jul 07 2018 08:51:39
%S A208866 2,12,143,1979,28246,405481,5826959,83752328,1203835147,17303737555,
%T A208866 248721498050,3575088704597,51387836750983,738641752044964,
%U A208866 10617135747615911,152609260439813291,2193584684852893774
%N A208866 Number of n X 2 0..3 arrays with new values 0..3 introduced in row major order and no element equal to more than one of its immediate leftward or upward or right-upward antidiagonal neighbors.
%C A208866 Column 2 of A208872.
%H A208866 R. H. Hardin, <a href="/A208866/b208866.txt">Table of n, a(n) for n = 1..210</a>
%F A208866 Empirical: a(n) = 18*a(n-1) - 55*a(n-2) + 42*a(n-3) - 9*a(n-4) for n>5.
%F A208866 Empirical g.f.: x*(2 - 24*x + 37*x^2 - 19*x^3 + 3*x^4) / ((1 - 3*x + x^2)*(1 - 15*x + 9*x^2)). - _Colin Barker_, Jul 07 2018
%e A208866 Some solutions for n=4:
%e A208866 ..0..0....0..0....0..0....0..0....0..0....0..0....0..0....0..1....0..1....0..0
%e A208866 ..1..0....1..0....1..0....1..1....1..0....1..0....1..1....1..2....1..2....1..1
%e A208866 ..1..2....1..0....1..1....0..0....0..2....0..1....2..1....3..3....0..1....2..0
%e A208866 ..3..2....2..2....2..0....1..0....1..3....1..2....0..3....0..1....0..0....1..1
%Y A208866 Cf. A208872.
%K A208866 nonn
%O A208866 1,1
%A A208866 _R. H. Hardin_, Mar 02 2012