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A140839
Number of inequivalent indecomposable regular SQ matrices (strongly quadrangular) of order n.
0
1, 1, 1, 2, 2, 4
OFFSET
1,4
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.
CROSSREFS
Sequence in context: A006560 A088251 A229627 * A320299 A357969 A292943
KEYWORD
nonn
AUTHOR
Jonathan Vos Post, Jul 18 2008
STATUS
approved