# [seqfan] Re: unable to reproduce A152218 (sigma divisibility)

c.zizka at email.cz c.zizka at email.cz
Wed Aug 25 16:28:33 CEST 2010

```Hi Jack,
you are right, this should be  :

A152218  sigma_2(n)*sigma_1(n)/sigma_0(n)=c, c is a square.

Have a nice day,

Ctibor O. Zizka

> ------------ Původní zpráva ------------
> Od: Jack Brennen <jfb at brennen.net>
> Předmět: [seqfan] Re: unable to reproduce A152218 (sigma divisibility)
> Datum: 25.8.2010 01:26:10
> ----------------------------------------
> A152218 seems to be those numbers for which:
>
> sigma_2(n)/sigma(n)/tau(n) is a square of a rational.
>
> At least that definition agrees out through those first 8 terms.
>
> That of course is a fairly different description that what is
> actually shown there.  :)
>
> Richard Mathar wrote:
> > I can reproduce A152215, but the very similar A152218 seems to
> > be missing almost all terms:
> >
> > http://oeis.org/classic/A152218
> > Numbers such that sigma_2(n) * sigma(n) /tau(n) = integer
> > 1, 4, 529, 2116, 2583, 3249, 3346, 6150
> > What is a definition that matches the sequence?
> > The formula says the same as the definition, so it is no aid.
> >
> > The values sigma_2(n) * sigma(n) /tau(n) are
> > 1, 15/2, 20, 49, 78, 150, 200, 1275/4, 1183/3, 585, 732, 980, 1190, 1500,
> 1560, 10571/5
> > and most of these are integers
> >
> > RJM
> >
> >
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> >
> >
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```