[seqfan] Re: A001495

[David Newman]

Thanks.  I couldn't have understood that from the title.

On Sun, Aug 4, 2013 at 1:52 PM, <israel at math.ubc.ca> wrote:

> This seems to be what Gupta's article calls gamma^*(n+1), the number of
> (n+1) x (n+1) symmetric 0-1 matrices with row sums 2 and first row
> (1,1,0,...). Thus A(3) = 3 because there are 3 symmetric 4 x 4 0-1 matrices
> with row sums 2 and first row 1 1 0 0, namely
>
> 1100
> 1001
> 0011
> 0110
>
> 1100
> 1010
> 0101
> 0011
>
> and
>
> 1100
> 1100
> 0011
> 0011
>
> Cheers,
> Robert
>
>
> On Aug 4 2013, David Newman wrote:
>
>  This sequence is titled Number of Stochastic Matrices of Integers and it
>> begins
>>
>> 1,1,1,3,13,70.  I don't understand this.  It seems to me that for n=2
>> there
>> are two matrices of non-negative integers with row sums 1 and column sums
>> of 1, namely
>>
>> ((1,0),(0,1)) and ((0,1),(1,0)). So a(2) should be 2, not 1.   There is a
>> reference to an article called "Enumeration of Symmetric Matrices', but I
>> don't have access to this.  Can someone explain to me what is being
>> counted
>> by this sequence?
>>
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