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%I #7 Sep 06 2013 02:04:51
%S 9,390,20160,1106424,62606544,3611217792,211096262400,12461757863808,
%T 741242882016000,44355068641175040,2667095701669969920,
%U 161021441731743129600,9754428938330096713728,592621128107578217201664
%N Number of pairs of orthogonal (-1,2) vectors of length 3*n.
%C Row 2 of A225987.
%H R. H. Hardin, <a href="/A225988/b225988.txt">Table of n, a(n) for n = 1..202</a>
%e All solutions for n=1
%e .-1.-1...-1..2...-1..2...-1..2....2..2...-1..2...-1.-1....2..2...-1..2
%e .-1..2...-1.-1....2.-1....2..2...-1..2....2..2...-1.-1...-1..2...-1..2
%e .-1.-1...-1.-1....2..2....2.-1....2.-1...-1..2...-1..2...-1..2....2..2
%K nonn
%O 1,1
%A _R. H. Hardin_, May 22 2013