0,5

More precisely, number of inequivalent Hadamard matrices of order n if two matrices are considered equivalent if one can be obtained from the other by permuting rows, permuting columns and multiplying rows or columns by -1.

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

J. Hadamard, R\'{e}solution d'une question relative aux d\'{e}terminants, Bull. des Sciences Math. 2 (1893), 240-246.

Kimura, H., (1986), Hadamard matrices of order 28 with automorphism groups of order two, J. Combin. Theory, A 43, 98-102.

Kimura, H., (1989), New Hadamard matrix of order 24, Graphs Combin., 5, 235-242.

Kimura, H., (1994), Classification of Hadamard matrices of order 28 with Hall sets, Discrete Math., 128, 257-268.

Kimura, H., (1994), Classification of Hadamard matrices of order 28, Discrete Math., 133, 171-180.

W. P. Orrick, Switching operations for Hadamard matrices, http://arXiv.org/abs/math.CO/0507515. (Gives lower bounds for a(8) and a(9))

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

Wolfram, S. A New Kind of Science. Champaign, IL: Wolfram Media, p. 1073, 2002.

N. J. A. Sloane, Tables of Hadamard matrices

N. J. A. Sloane, My favorite integer sequences, in Sequences and their Applications (Proceedings of SETA '98).

Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.

Cf. A096201, A036297, A048615, A048616, A003432.

Sequence in context: A038245 A027858 A124013 this_sequence A109254 A145985 A048885

Adjacent sequences: A007296 A007297 A007298 this_sequence A007300 A007301 A007302

hard,nonn,nice

N. J. A. Sloane (njas(AT)research.att.com).