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A208858 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 left-upward diagonal neighbors.

%I A208858 #9 Jul 07 2018 06:13:32
%S A208858 2,11,127,1691,23047,315203,4313071,59022155,807696535,11053048211,
%T A208858 151257183487,2069902880411,28325913895207,387630456564323,
%U A208858 5304590398318351,72591507756551915,993389989178417335
%N A208858 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 left-upward diagonal neighbors.
%C A208858 Column 2 of A208864.
%H A208858 R. H. Hardin, <a href="/A208858/b208858.txt">Table of n, a(n) for n = 1..210</a>
%F A208858 Empirical: a(n) = 17*a(n-1) - 48*a(n-2) + 36*a(n-3) for n>4.
%F A208858 Empirical g.f.: x*(2 - 23*x + 36*x^2 - 12*x^3) / ((1 - 2*x)*(1 - 15*x + 18*x^2)). - _Colin Barker_, Jul 07 2018
%e A208858 Some solutions for n=4:
%e A208858 ..0..0....0..0....0..0....0..0....0..1....0..0....0..0....0..0....0..0....0..1
%e A208858 ..0..1....0..1....1..1....1..1....1..0....0..1....0..1....1..1....0..1....1..2
%e A208858 ..0..2....1..0....0..2....2..0....0..1....0..1....1..2....0..0....1..0....3..3
%e A208858 ..1..3....1..2....2..0....1..2....0..1....0..2....2..0....0..1....2..2....3..1
%Y A208858 Cf. A208864.
%K A208858 nonn
%O A208858 1,1
%A A208858 _R. H. Hardin_, Mar 02 2012