%I #6 Aug 12 2016 06:54:16
%S 1,21,145,1122,7886,58446,405196,2865756,19652430,135666717,917861737,
%T 6247996468,41874859669,281884085368,1877330322718,12537690094009,
%U 83063782595536,551574419251898,3639691674489757,24059481994135080
%N Number of 3Xn arrays containing n copies of 0..3-1 with row sums and column sums nondecreasing.
%C Row 3 of A267990.
%H R. H. Hardin, <a href="/A267992/b267992.txt">Table of n, a(n) for n = 1..30</a>
%e Some solutions for n=6
%e ..1..0..1..0..0..1....0..1..1..2..1..0....0..2..0..0..1..2....0..1..2..0..0..0
%e ..1..0..0..2..2..2....0..1..2..0..0..2....0..0..1..1..1..2....1..0..1..1..2..1
%e ..0..2..1..1..2..2....2..1..0..1..2..2....1..0..1..2..2..2....2..2..0..2..1..2
%Y Cf. A267990.
%K nonn
%O 1,2
%A _R. H. Hardin_, Jan 23 2016