Re Permanents of (+1,-1) matrices

[Jaap Spies]

N. J. A. Sloane wrote:

> 
> So here is a (hard) question:  can you solve the 5x5 case?
> Is 24 the max permanent of an invertible 5x5 +-1 matrix?
> 
> (I don't know if this is already proved by some other
> method than exhaustive search)
> 

Yes,i I did an exhaustive search on all 5x5 (-1,1) matrices:

no permanents > 24 for non-singular matrices.

For the case 4x4 I found 384 non-singular matrices with permanent=8.

Jaap Spies