A001119 Number of skew-symmetric Hadamard matrices of order 4n.

1, 1, 2, 2, 16, 54

Offset

2,3

Links

Table of n, a(n) for n=2..7.

F. J. Aragon Artacho, J. M. Borwein, M. K. Tam, Douglas-Rachford Feasibility Methods for Matrix Completion Problems, March 2014.

J. Gebel, Integer points on Mordell curves [Cached copy, after the original web site tnt.math.se.tmu.ac.jp was shut down in 2017]

Joseph W. Iverson, John Jasper, and Dustin G. Mixon, More on the optimal arrangement of 2d lines in C^d, arXiv:2410.17379 [math.MG], 2024. See p. 21.

C. Koukouvinos and S. Stylianou, On skew-Hadamard matrices, Discrete Math., 308 (2008), 2723-2731.

Edward Spence, Classification of Hadamard matrices of order 24 and 28, Discrete Math. 140 (1995), no. 1-3, 185-243.

Crossrefs

Sequence in context: A098777 A127226 A371548 * A216387 A062282 A230990

Adjacent sequences: A001116 A001117 A001118 * A001120 A001121 A001122

Keyword

nonn,hard,more,nice

Author

N. J. A. Sloane.

Status

approved