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%I #4 May 17 2012 14:37:12
%S 30,486,7862,126606,2034200,32644314,523487828,8390738062,
%T 134446993320,2153764911576,34495886876214,552428007496418,
%U 8845775486728392,141630619844515292,2267494906950636872,36300174404152871822
%N Number of 0..3 arrays of length 2*n+1 with sum no more than 3*n in any length 2n subsequence (=50% duty cycle)
%C Row 2 of A212471
%H R. H. Hardin, <a href="/A212473/b212473.txt">Table of n, a(n) for n = 1..210</a>
%e Some solutions for n=3
%e ..0....2....2....2....0....1....0....1....0....0....2....2....1....3....0....0
%e ..0....0....0....0....0....1....3....1....0....1....2....0....0....0....1....1
%e ..2....3....2....1....2....0....0....0....1....1....3....0....1....0....1....3
%e ..1....3....3....0....0....3....1....0....1....3....0....1....0....0....0....0
%e ..2....0....1....3....1....2....2....1....1....0....0....1....1....1....0....3
%e ..0....0....1....1....2....2....1....3....2....0....1....0....0....2....1....0
%e ..2....0....2....1....2....1....2....0....1....0....1....0....0....0....2....2
%K nonn
%O 1,1
%A _R. H. Hardin_ May 17 2012
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