Q. about {0,1}-matrices.

[Brendan McKay]

* Edwin Clark <eclark at math.usf.edu> [070107 09:08]:
> On Sat, 6 Jan 2007, Ferenc Adorjan wrote:
> 
> > Hello Neil and Seqfans,
> > 
> > I have composed a Pari program to determine the number of nxn robust
> > 0,1 matrices.
> > Certainly, the program below is neither optimal nor verfied. It
> > provides properly the value of 4 and 68, but as the fourth term it
> > gives 5440 instead of the value in your sequence (5008).
> > Somebody should verify the program (or the term #4) before anybody
> > tries to calculate the fifth term.
> > Ferenc
> 
> I wrote a Maple program to calculate nxn robust matrices. It
> agrees with the values 1, 4, 68, 5008 given by Neil. It is
> now using those 5008 of size 4x4 to compute the number of
> 5x5's. At the present rate it should be done in about 5 more
> hours. 

I did it in C and got 1, 4, 68, 5008, 1603232 in one second.
Maybe the next one will be done in an hour or so.  I expect
it will be 1-2 billion, and someone should check it.
a(6) is not impossible but would need a good reason.
 
Brendan.