[seqfan] Re: A133579

Neil Sloane njasloane at gmail.com
Sat Feb 14 03:13:06 CET 2015


First, about A133580: the definition was correct, and the terms were
correct, but the offset should have been 0.  I changed the offset and added
some example lines to clarify the situation.

The b-file is now wrong, unfortunately (Harvey, could you correct it?), and
probably the programs also need correcting.

Following Franklin's hint, this suggests that the correct
definition of A133579 should be:

a(0)=a(1)=1; for n>1, a(n) = 3*a(n-1)  if a(n-1) and n are coprime,
otherwise a(n) = a(n-1)/gcd(a(n-1),n).

This almost matches the terms, but there is a mistake at
a(6), I believe, - as Harvey noticed - so it
needs to be recomputed. (a(6) should be 1 not 9). The offset is also wrong,
it should be 0, and I will fix that.

Best regards
Neil

Neil J. A. Sloane, President, OEIS Foundation.
11 South Adelaide Avenue, Highland Park, NJ 08904, USA.
Also Visiting Scientist, Math. Dept., Rutgers University, Piscataway, NJ.
Phone: 732 828 6098; home page: http://NeilSloane.com
Email: njasloane at gmail.com


On Fri, Feb 13, 2015 at 8:33 PM, Frank Adams-Watters <franktaw at netscape.net>
wrote:

> The definition is clearly wrong, since gcd(n,a(n-1)) always divides a(n-1).
>
> A133580 seems to be related, and may provide a clue. (BTW, the offset for
> A133580 is wrong; from the definition it should be 0.)
>
> Franklin T. Adams-Watters
>
>
> -----Original Message-----
> From: Harvey P. Dale <hpd at hpdale.org>
> To: Sequence Fanatics Discussion list <seqfan at list.seqfan.eu>
> Sent: Fri, Feb 13, 2015 6:59 pm
> Subject: [seqfan] A133579
>
>
>         I cannot figure out how to generate the terms of the above
> sequence from its
> definition.
>         Best,
>         Harvey
>
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