%I
%S 246,5211,93308,1581686,26242268,430682205,7023308036,114062278982,
%T 1847205725100,29854017540652,481755564098784,7764949351300178,
%U 125039067197089316,2011992600375317822,32354843213417739992
%N Number of 0..3 arrays of length 2*n+3 with sum no more than 3*n in any length 2n subsequence (=50% duty cycle)
%C Row 4 of A212471
%H R. H. Hardin, <a href="/A212475/b212475.txt">Table of n, a(n) for n = 1..210</a>
%e Some solutions for n=3
%e ..1....2....1....1....3....2....3....2....2....0....0....1....1....1....1....0
%e ..1....0....0....0....1....1....2....1....1....0....1....1....1....0....1....0
%e ..0....0....2....1....0....0....3....1....0....0....2....3....0....0....1....2
%e ..0....0....3....2....2....3....1....0....0....1....1....0....0....2....1....2
%e ..2....1....0....3....0....0....0....3....0....1....1....2....3....0....3....0
%e ..0....0....1....0....2....0....0....1....3....2....0....0....1....0....0....1
%e ..3....2....1....0....0....2....0....1....1....1....0....0....0....1....1....0
%e ..0....0....0....0....1....3....3....2....1....0....2....2....2....2....1....3
%e ..3....3....3....3....1....0....2....1....1....0....3....1....2....2....3....3
%K nonn
%O 1,1
%A _R. H. Hardin_ May 17 2012
