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%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
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