# [seqfan] Re: G.f. for trees with degree at most 3

franktaw at netscape.net franktaw at netscape.net
Mon May 24 07:07:30 CEST 2010

It's not a divisibility sequence. I assume you meant the right-shifted
sequence; as it is,a(3) = 16 does not divide a(6) = 14070.  However,
the right-shifted sequence is also not a divisibility sequence; for it,
a(6) = 1170 does not divide a(12) = 32212857600.

-----Original Message-----
From: Richard Guy <rkg at cpsc.ucalgary.ca>

It looks as though it is a divisibility sequence.  Could
someone check if it satisfies a linear recurrence of order
6 or less?  (or more, but that would be very tentative)  R.

On Sun, 23 May 2010, franktaw at netscape.net wrote:

> I asked the author of this sequence for clarification, but got no >
response. Maybe somebody here can figure out what is going on.
>
> http://www.research.att.com/~njas/sequences/A003692
>
> For this sequence, a generating function is given:
>
> (1-x)(2-x-x^2) - (2-x+x^2)\sqrt{1-2x-x^2} \over 3 x^3.
>
> I'm not sure if this is supposed to be
>
> (1-x)*(2-x-x^2)-(2-x-x^2)*sqrt(1-2*x-x^2)/(3*x^3)
>
> or
>
> ((1-x)*(2-x-x^2)-(2-x-x^2)*sqrt(1-2*x-x^2))/(3*x^3),
>
> but either one produces a series that includes terms with negative >
exponents; and in neither case there is any apparent relationship to >
this sequence. So what is the correct g.f.?
>
>
> >
>
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>
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