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A140838
Number of inequivalent symmetric SQ matrices (strongly quadrangular) of order n.
0
1, 2, 4, 11, 44
OFFSET
1,2
COMMENTS
Abstract: Strongly quadrangular matrices have been introduced in the study of the combinatorial properties of unitary matrices. It is known that if a (0, 1)-matrix supports a unitary then it is strongly quadrangular. However, the converse is not necessarily true. In this paper, we fully classify strongly quadrangular matrices up to degree 5. We prove that the smallest strongly quadrangular matrices which do not support unitaries have exactly degree 5. Further, we isolate two submatrices not allowing a (0, 1)-matrix to support unitaries.
LINKS
Simone Severini and Ferenc Szollosi, A further look into combinatorial orthogonality, arXiv:0709.3651
CROSSREFS
Sequence in context: A213937 A328437 A107703 * A114954 A134019 A120259
KEYWORD
nonn
AUTHOR
Jonathan Vos Post, Jul 18 2008
STATUS
approved