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A225987 T(n,k)=Number of pairs of orthogonal (-x,y) vectors of length k*(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 ...

%I A225987 #6 Oct 13 2021 06:08:12
%S A225987 4,48,9,640,390,20,8960,20160,3192,60,129024,1106424,652784,48720,45,
%T A225987 1892352,62606544,134432480,41801760,26010,420,28114944,3611217792,
%U A225987 28244153600,36951200000,21594300,8168160,102,421724160,211096262400
%N A225987 T(n,k)=Number of pairs of orthogonal (-x,y) vectors of length k*(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 A225987 Table starts
%C A225987 ..4....48......640........8960.........129024...........1892352
%C A225987 ..9...390....20160.....1106424.......62606544........3611217792
%C A225987 .20..3192...652784...134432480....28244153600.....6052498776192
%C A225987 .60.48720.41801760.36951200000.33792065269760.31520952625612800
%C A225987 .45.26010.21594300.15593341800.11432293516320..8690522384325600
%H A225987 R. H. Hardin, <a href="/A225987/b225987.txt">Table of n, a(n) for n = 1..1056</a>
%e A225987 Some solutions for n=1 k=4
%e A225987 .-1..1....1..1...-1.-1...-1.-1...-1..1....1..1...-1..1...-1.-1...-1.-1...-1..1
%e A225987 ..1..1...-1.-1...-1..1...-1..1....1..1...-1..1...-1.-1...-1..1...-1..1...-1.-1
%e A225987 .-1..1...-1..1....1..1...-1.-1...-1..1....1.-1....1.-1...-1.-1....1.-1....1.-1
%e A225987 .-1.-1...-1.-1....1.-1...-1.-1....1..1...-1.-1....1.-1...-1..1....1.-1....1.-1
%e A225987 ..1.-1....1.-1...-1.-1....1.-1...-1.-1...-1.-1....1..1...-1..1...-1..1...-1.-1
%e A225987 ..1.-1...-1..1....1..1....1..1...-1..1....1.-1....1.-1...-1.-1...-1.-1...-1.-1
%e A225987 ..1..1....1..1...-1..1....1.-1....1.-1....1.-1....1..1....1..1...-1.-1...-1.-1
%e A225987 ..1..1....1.-1...-1..1...-1..1...-1.-1...-1.-1....1..1....1.-1...-1.-1....1.-1
%Y A225987 Row 1 is A098402.
%K A225987 nonn,tabl
%O A225987 1,1
%A A225987 _R. H. Hardin_, May 22 2013