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A140836 Number of inequivalent SQ matrices (strongly quadrangular) of order n. 0
1, 2, 4, 15, 80 (list; graph; refs; listen; history; text; internal format)
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

Table of n, a(n) for n=1..5.

Simone Severini and Ferenc Szollosi, A further look into combinatorial orthogonality, arXiv:0709.3651

CROSSREFS

Sequence in context: A290024 A292757 A182449 * A020134 A307085 A228934

Adjacent sequences:  A140833 A140834 A140835 * A140837 A140838 A140839

KEYWORD

nonn

AUTHOR

Jonathan Vos Post, Jul 18 2008

STATUS

approved

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Last modified March 28 11:00 EDT 2020. Contains 333083 sequences. (Running on oeis4.)