A118992 Number of real n X n invertible symmetric (+1,-1) matrices.

2, 4, 32, 512, 16896, 1190144, 163899904, 46195853312, 25585116626944, 28281621931343872

Offset: 1

Author

Giovanni Resta, May 08 2006

Keywords

• nonn
• more

Crossrefs

Cf. A056990, A086899, A056989, A118990, A118993, A118994, A118997.

Formula

a(n) = 2^(n*(n+1)/2) - A118990(n) = A118994(n) + A118997(n). - Max Alekseyev, Jun 12 2025

Extensions

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