# [seqfan] Re: seq needed of (0,+-1) matrices

Ron Hardin rhhardin at att.net
Thu Jan 19 20:53:06 CET 2012

```I get 1 3 27 293 3605 52327 899311
unless I've misunderstood the formula
(does "... (*)" mean anything?  I'm worried because it suggests a continuation)

rhhardin at mindspring.com
rhhardin at att.net (either)

----- Original Message ----
> From: Max Alekseyev <maxale at gmail.com>
> To: Sequence Fanatics Discussion list <seqfan at list.seqfan.eu>
> Cc: seqfan at seqfan.eu; njas at research.att.com
> Sent: Wed, January 18, 2012 4:03:09 PM
> Subject: [seqfan] Re: seq needed of (0,+-1) matrices
>
> The first 6 terms of the requested sequence are:
>
> 1, 3, 27, 125, 461,  1583
>
> I may also get a(7) soon.
>
> Regards,
> Max
>
> On Wed, Jan  18, 2012 at 1:16 PM, N. J. A. Sloane <njas at research.att.com>
>wrote:
> >
> > Dear Seq Fans, This paper:
> >
> > MR2002770  (2004g:05108)
> > Wesp, Gerhard(A-SALZ-IM)
> > A note on the spectra of  certain skew-symmetric {1,0,1}-matrices. (English
>summary)
> > Discrete  Math. 258 (2002), no. 1-3, 339-346.
> >
> > discusses matrices A =  (a_ij) of size nxn with entries from {-1,0,+1}
> > which are skew-symmetric  and have the additional property that
> >
> > a_wx a_yz + a_wy a_zx +  a_wz a_xy = a_wx a_wy a_wz a_xy a_xz a_yz ... (*)
> >
> > for all  distinct w,x,y,z in {1..n}.
> >
> > But he does not count them. Can  someone compute the first few terms?
> > Obviously a(1)=1 (the zero  matrix),
> > a(2) = 3, a(3) = 27 (up to this point we get all skew-symmetric  matrices)
> > and a(4) < 3^6
> >
> > (There seem to be several  combinatorial applications)
> >
> > Neil
> >
> >
> >  _______________________________________________
> >
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>
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>

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