A352177 - OEIS

%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