ELA, Volume 5, pp. 19-23, February 1999, abstract.
The Possible Numbers of Zeros in an Orthogonal Matrix
G.-S. Cheon, C. R. Johnson, S.-G. Lee, and E. J. Pribble
It is shown that for n greater than or equal to 2 there is an n by n
indecomposable orthogonal matrix with exactly k entries equal to zero
if and only if k is greater than or equal to 0 and less than or equal
to (n-2) squared