[seqfan] Re: oddness of iterations of sigma()
Harvey P. Dale
hpd at hpdale.org
Tue Nov 12 16:09:10 CET 2013
In response to the first question, there are no such odd numbers up to 50 million.
From: SeqFan [mailto:seqfan-bounces at list.seqfan.eu] On Behalf Of Max Alekseyev
Sent: Tuesday, November 12, 2013 8:59 AM
Subject: [seqfan] oddness of iterations of sigma()
Vladimir Letsko is unfortunate in his attempts to join SeqFan maillist.
So he asked me to forward his question; please 'carbon copy' your replies to his email.
---------- Forwarded message ----------
From: Letsko Vladimir <val-etc at yandex.ru>
Does anybody know the answer on some questions associated with A231484?
1. Does there exists an odd number n > 1 for which sigma(n),
sigma(sigma(n)) and sigma(sigma(sigma(n))) are odd too?
2. Does there exists a number n > 1 such that sigma(sigma(sigma(n)))/n < 1.5?
3. Note that sigma(3^4) = 11^2. Does there exists another pair (p,r) such that p is prime, r > 1 and sigma(p^r) = q^s where q is prime and s > 1?
Seqfan Mailing list - http://list.seqfan.eu/
More information about the SeqFan