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 A225986 Number of pairs of orthogonal (-x,y) vectors of length 1*(x+y), where x/y is the n-th rational <= 1, ordered first by y and then x, e.g. 1/1, 1/2, 1/3, 2/3, 1/4, 3/4 ... 1
 4, 9, 20, 60, 45, 420, 102, 378, 1120, 3024, 231, 22176, 520, 2376, 8160, 23760, 63360, 164736, 1161, 21780, 185328, 1235520, 2570, 14190, 188760, 544544, 3660800, 9335040, 5643, 147576, 11202048, 70946304, 12300, 80028, 374192, 1408680 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Column 1 of A225987 LINKS R. H. Hardin, Table of n, a(n) for n = 1..210 EXAMPLE All solutions for n=1 .-1..1...-1.-1...-1..1....1..1 .-1.-1...-1..1....1..1...-1..1 CROSSREFS Sequence in context: A111587 A161221 A130045 * A147971 A197869 A276319 Adjacent sequences:  A225983 A225984 A225985 * A225987 A225988 A225989 KEYWORD nonn AUTHOR R. H. Hardin May 22 2013 STATUS approved

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Last modified January 19 06:18 EST 2022. Contains 350464 sequences. (Running on oeis4.)