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

9, 390, 20160, 1106424, 62606544, 3611217792, 211096262400, 12461757863808, 741242882016000, 44355068641175040, 2667095701669969920, 161021441731743129600, 9754428938330096713728, 592621128107578217201664

Offset: 1

Author

R. H. Hardin, May 22 2013

Keywords

• nonn

Comments

Row 2 of A225987.

Examples

			All solutions for n=1
.-1.-1...-1..2...-1..2...-1..2....2..2...-1..2...-1.-1....2..2...-1..2
.-1..2...-1.-1....2.-1....2..2...-1..2....2..2...-1.-1...-1..2...-1..2
.-1.-1...-1.-1....2..2....2.-1....2.-1...-1..2...-1..2...-1..2....2..2
		

Links

• R. H. Hardin, Table of n, a(n) for n = 1..202