%I #4 Jun 12 2012 07:45:25

%S 31,927,18018,319078,5444644,91147915,1508740928,24791568796,

%T 405322707108,6602565936460,107259549395070,1738767957760734,

%U 28139860212492988,454796793295838938,7342320714558321488

%N Number of 0..3 arrays of length 2*n+2 with sum less than 3*n in any length 2n subsequence (=less than 50% duty cycle)

%C Row 3 of A213464

%H R. H. Hardin, <a href="/A213467/b213467.txt">Table of n, a(n) for n = 1..210</a>

%e Some solutions for n=3

%e ..3....2....1....1....3....0....0....1....0....1....3....0....1....0....3....2

%e ..0....0....1....0....0....2....0....3....1....2....0....0....0....0....1....1

%e ..0....1....0....0....0....0....2....0....0....2....1....2....1....0....1....2

%e ..1....2....1....0....1....2....0....0....3....1....0....2....0....1....0....0

%e ..0....0....0....1....2....0....2....3....0....1....1....3....1....0....2....2

%e ..3....2....1....0....1....0....0....0....2....0....3....0....3....1....0....0

%e ..1....1....1....2....2....2....2....0....1....1....0....0....2....2....0....2

%e ..1....1....0....3....2....1....0....1....0....3....2....1....0....1....0....0

%K nonn

%O 1,1

%A _R. H. Hardin_ Jun 12 2012