A001121 Number of doubly-regular tournaments of order 4n-1.

1, 1, 2, 2, 37, 722

Offset

2,3

Comments

Equally, number of skew digraphs in switching classes of Hadamard matrices of order 4n.

Links

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

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]

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

Crossrefs

Sequence in context: A267345 A059523 A038623 * A202711 A222668 A210246

Adjacent sequences: A001118 A001119 A001120 * A001122 A001123 A001124

Keyword

nonn,hard,more,nice

Author

N. J. A. Sloane

Extensions

Better name suggested by Brendan McKay, Oct 31 2007

Status

approved