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A225988 Number of pairs of orthogonal (-1,2) vectors of length 3*n. 1

%I

%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

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Last modified January 28 21:13 EST 2022. Contains 350664 sequences. (Running on oeis4.)