%I #15 Dec 13 2023 08:32:56
%S 1,2,1,2,1,3,1,1,2,1,1,1,1,1,1,1,1,1,1
%N a(n) is the number of symmetric Toeplitz anti-Hadamard matrices of order n whose sum of the inverse squares of their singular values is maximal.
%H R. L. Graham and N. J. A. Sloane, <a href="http://dx.doi.org/10.1016/0024-3795(84)90090-9">Anti-Hadamard matrices</a>, Linear Alg. Applic., 62 (1984), 113-137.
%F Conjectures: (Start)
%F a(n) = 1 for n > 9.
%F G.f.: x*(x + x^3 + 2*x^5 + x^8 + 1/(1 - x)). (End)
%Y Cf. A351240, A351241.
%Y Cf. A005312, A005313, A351821, A351984.
%K nonn,hard,more
%O 1,2
%A _Stefano Spezia_, Mar 08 2022