A001111 - OEIS

%I #23 Sep 19 2023 05:13:27

%S 1,1,1,5,6,1106,208310,10374196953

%N Number of inequivalent Hadamard designs of order 4n.

%C In other words, number of 2-(4*n-1,2*n-1,n-1) symmetric designs.

%H R. K. Guy, <a href="/A002186/a002186.pdf">Letters to N. J. A. Sloane, June-August 1968</a>.

%H Edward Spence, <a href="https://web.archive.org/web/20071123155400/http://www.maths.gla.ac.uk/~es/hadamard.html">Hadamard matrices</a>.

%H Edward Spence, <a href="http://dx.doi.org/10.1016/0012-365X(93)E0169-5">Classification of Hadamard matrices of order 24 and 28</a>, Discrete Math. 140 (1995), no. 1-3, 185-243.

%H <a href="/index/Ha#Hadamard">Index entries for sequences related to Hadamard matrices</a>

%K nonn,hard,nice,more

%O 1,4

%A _N. J. A. Sloane_

%E a(8) from _Brendan McKay_, Feb 11 2012