A351984 a(n) is the number of symmetric anti-Hadamard matrices of order n whose sum of the inverse squares of their singular values is maximal.

1, 2, 6, 24, 120, 840, 5040

Offset

1,2

Comments

The sequence of the ratio a(n+1)/a(n) begins with 2, 3, 4, 5, 7, 6, ...

Is a(n+1)/a(n) integer for all n? If that is true, excluding the number 1, is the sequence of the ratio a(n+1)/a(n) a permutation of all other natural numbers?

Links

Table of n, a(n) for n=1..7.

R. L. Graham and N. J. A. Sloane, Anti-Hadamard matrices, Linear Alg. Applic., 62 (1984), 113-137.

Crossrefs

Cf. A005312, A005313, A119002, A351153.

Sequence in context: A114790 A352430 A292749 * A365977 A079854 A024923

Adjacent sequences: A351981 A351982 A351983 * A351985 A351986 A351987

Keyword

nonn,hard,more

Author

Stefano Spezia, Feb 27 2022

Status

approved