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A140838 Number of inequivalent symmetric SQ matrices (strongly quadrangular) of order n. 0
1, 2, 4, 11, 44 (list; graph; refs; listen; history; text; internal format)



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.


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

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


Sequence in context: A213937 A328437 A107703 * A114954 A134019 A120259

Adjacent sequences:  A140835 A140836 A140837 * A140839 A140840 A140841




Jonathan Vos Post, Jul 18 2008



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Last modified December 6 08:53 EST 2019. Contains 329788 sequences. (Running on oeis4.)