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 A225988 Number of pairs of orthogonal (-1,2) vectors of length 3*n. 1
 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 A266924 Adjacent sequences:  A225985 A225986 A225987 * A225989 A225990 A225991 KEYWORD nonn AUTHOR R. H. Hardin, May 22 2013 STATUS approved

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Last modified February 22 15:52 EST 2019. Contains 320399 sequences. (Running on oeis4.)