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From: bdm@anucsd.UUCP
Newsgroups: net.math
Subject: Re: Combinatorics question...
Message-ID: <269@anucsd.OZ>
Date: Thu, 13-Mar-86 23:33:08 EST
Article-I.D.: anucsd.269
Posted: Thu Mar 13 23:33:08 1986
Date-Received: Mon, 17-Mar-86 04:42:36 EST
References: <736@harvard.UUCP>
Organization: Computer Science, Australian National Uni, Canberra
Lines: 21

In article <736@harvard.UUCP>, greg@harvard.UUCP (Greg) writes:
> 
> How many 8x8 matrices of 0's and 1's are there in which each row and column
> has precisely four 1's?
 
(continuation of earlier response)

If one only considers equivalence classes of such matrices under the operations
of row permutation, column permutation and transpose, there are exactly 130
cases.  This was determined about 1976 by I.A.Faradzev using exhaustive
enumeration.
 
 Brendan McKay.
 Computer Science Department, Australian National University,
 GPO Box 4, Canberra, ACT 2601, Australia.

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