%I #9 Aug 12 2016 07:04:23
%S 1,4,36,648,19800,972000,69060600,6756825600,866219961600,
%T 140837901120000,28269530815680000,6865910948635200000
%N Number of nX2 arrays containing 2 copies of 0..n-1 with column sums equal.
%C Column 2 of A268472.
%e Some solutions for n=4
%e ..3..1. .1..1. .2..1. .1..0. .0..0. .3..2. .0..3. .3..3. .2..2. .1..2
%e ..1..3. .0..3. .1..3. .2..3. .2..3. .0..3. .1..0. .2..0. .3..3. .0..0
%e ..0..0. .3..2. .3..2. .0..1. .1..2. .1..0. .3..1. .1..2. .1..1. .2..3
%e ..2..2. .2..0. .0..0. .3..2. .3..1. .2..1. .2..2. .0..1. .0..0. .3..1
%Y Cf. A268472.
%K nonn
%O 1,2
%A _R. H. Hardin_, Feb 05 2016