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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.
2
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
R. L. Graham and N. J. A. Sloane, Anti-Hadamard matrices, Linear Alg. Applic., 62 (1984), 113-137.
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Stefano Spezia, Feb 27 2022
STATUS
approved