A225986 - OEIS

%I #5 May 22 2013 12:59:33

%S 4,9,20,60,45,420,102,378,1120,3024,231,22176,520,2376,8160,23760,

%T 63360,164736,1161,21780,185328,1235520,2570,14190,188760,544544,

%U 3660800,9335040,5643,147576,11202048,70946304,12300,80028,374192,1408680

%N 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 ...

%C Column 1 of A225987

%H R. H. Hardin, <a href="/A225986/b225986.txt">Table of n, a(n) for n = 1..210</a>

%e All solutions for n=1

%e .-1..1...-1.-1...-1..1....1..1

%e .-1.-1...-1..1....1..1...-1..1

%K nonn

%O 1,1

%A _R. H. Hardin_ May 22 2013