A118997 Number of real n X n symmetric (+1,-1) matrices with negative determinant.

1, 4, 16, 80, 8448, 907904, 81949952, 13480664064, 12792558313472, 18963201072750592

Offset: 1

Author

Giovanni Resta, May 08 2006

Keywords

• nonn
• more

Crossrefs

Cf. A118999, A118992, A118994, A118996, A119000.

Formula

a(2n+1) = A118994(2n+1) = A118992(2n+1)/2. - Max Alekseyev, May 08 2009

a(n) = A118992(n) - A118994(n). - Max Alekseyev, Jun 12 2025

Extensions

a(8)-a(10) from Max Alekseyev, Jun 17 2025