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A140837
Number of inequivalent indecomposable symmetric SQ matrices (strongly quadrangular) of order n.
0
1, 1, 2, 6, 23
OFFSET
1,3
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: A341884 A377029 A213134 * A342860 A342840 A342861
KEYWORD
nonn
AUTHOR
Jonathan Vos Post, Jul 18 2008
STATUS
approved