[seqfan] Re: A001495

Neil Sloane njasloane at gmail.com
Mon Aug 5 06:40:41 CEST 2013


Robert,
thanks for clearing up that mystery. I'm traveling for
the next couple of weeks - could you do the necessary editing?
Thanks!
Neil


On Sun, Aug 4, 2013 at 1:30 PM, <israel at math.ubc.ca> wrote:

> Indeed.  This sequence really needs a new title and some comments.
>
>
> Cheers,
> Robert
>
> On Aug 4 2013, David Newman wrote:
>
>  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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-- 
Dear Friends, I have now retired from AT&T. New coordinates:

Neil J. A. Sloane, President, OEIS Foundation
11 South Adelaide Avenue, Highland Park, NJ 08904, USA
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Email: njasloane at gmail.com



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