21594300domain: NAppears in sequencesT(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 ...at n=25A225987Number of pairs of orthogonal (-1,4) vectors of length 5*n.at n=2A225991