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%I #6 May 02 2023 15:19:34
%S 85,1597,27024,445780,7274268,118029501,1908601444,30794657082,
%T 496095308012,7983014938756,128351434757356,2062286003105664,
%U 33118464621596452,531627920798750598,8530886270887938488
%N Number of 0..3 arrays of length 2*n+2 with sum no more than 3*n in any length 2n subsequence (=50% duty cycle).
%C Row 3 of A212471.
%H R. H. Hardin, <a href="/A212474/b212474.txt">Table of n, a(n) for n = 1..210</a>
%e Some solutions for n=3
%e ..0....0....1....2....2....0....2....2....1....2....1....1....1....2....0....3
%e ..0....0....2....0....0....0....2....0....0....1....1....0....0....1....1....0
%e ..1....2....1....1....1....1....1....3....2....0....0....1....0....2....3....2
%e ..0....1....0....1....3....2....0....0....2....0....0....0....3....0....0....0
%e ..2....1....0....0....2....1....0....1....2....0....1....0....0....0....0....1
%e ..2....0....1....1....1....0....3....1....0....1....2....2....0....0....0....1
%e ..1....2....3....3....2....3....3....2....0....2....3....1....3....0....3....2
%e ..1....2....1....2....0....2....0....0....1....2....3....2....1....3....0....2
%Y Cf. A212471.
%K nonn
%O 1,1
%A _R. H. Hardin_, May 17 2012
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