%I #9 Apr 19 2015 20:48:34
%S 15,71,175,327,987,2079,3603,9831,19947,33951,89787,180615
%N One-third of the number of n X n nonnegative integer arrays with every 3 X 3 subblock summing to 2.
%C Second differences of (a(3k), a(3k + 1), a(3k + 1)) and (a(3k + 1), a(3k + 2), a(3k + 3)) appear to be 48 * 9^(k - 1). Based on this conjecture, we would have a(15) = 306435. - _David A. Corneth_, Apr 15 2015
%K nonn,more
%O 3,1
%A _R. H. Hardin_, Sep 30 2008
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