A225988 - OEIS

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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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

Row 2 of A225987.

LINKS

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

EXAMPLE

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

CROSSREFS

Sequence in context: A157602 A124042 A297738 * A012191 A012078 A332139

Adjacent sequences: A225985 A225986 A225987 * A225989 A225990 A225991

KEYWORD

nonn

AUTHOR

R. H. Hardin, May 22 2013

STATUS

approved