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A217878 Number of n-element 0..2 arrays with each element the minimum of 3 adjacent elements of a random 0..2 array of n+2 elements.

%I A217878 #12 Feb 23 2018 11:28:51
%S A217878 3,9,22,46,91,183,383,819,1749,3699,7772,16316,34325,72349,152573,
%T A217878 321621,677623,1427389,3006930,6335210,13348399,28125235,59258363,
%U A217878 124851495,263048937,554220135,1167698552,2460253944,5183565225,10921353721
%N A217878 Number of n-element 0..2 arrays with each element the minimum of 3 adjacent elements of a random 0..2 array of n+2 elements.
%C A217878 See A228461 and A217883 for more information about the definition.
%H A217878 R. H. Hardin, <a href="/A217878/b217878.txt">Table of n, a(n) for n = 1..210</a>
%F A217878 Empirical: a(n) = 3*a(n-1) -3*a(n-2) +a(n-3) +3*a(n-4) -a(n-5) +a(n-6) +a(n-7).
%F A217878 Empirical g.f.: x*(1 + x^2 + x^3)*(3 + x^2 + x^3) / ((1 - x + x^2 + x^3)*(1 - 2*x - x^4)). - _Colin Barker_, Feb 23 2018
%e A217878 Some solutions for n=4:
%e A217878 ..0....1....0....0....2....1....1....1....0....1....2....0....0....0....1....0
%e A217878 ..0....1....2....0....1....1....2....2....1....1....2....1....1....0....2....1
%e A217878 ..0....2....0....0....1....1....0....2....2....0....2....1....1....2....1....2
%e A217878 ..2....2....0....1....1....1....0....1....1....0....1....1....2....2....1....0
%Y A217878 Column 3 of A217954. Also a column of A217883. Cf. A217954.
%K A217878 nonn
%O A217878 1,1
%A A217878 _R. H. Hardin_, Oct 14 2012