OFFSET
1,1
COMMENTS
This is a subsequence of the sequence of multiply perfect numbers A007691.
The prime values of sigma(n) / n are A219545.
Numbers whose abundancy index is a prime. There are two visible bends (sudden changes in the growth rate) in the scatter plot. Compare also to the scatter plot of A336702. - Antti Karttunen, Feb 25 2022
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..597 (computed from the b-file of A007691 prepared by T. D. Noe, using Flammenkamp's data)
PROG
(PARI) isA065997(n) = { my(p=sigma(n)/n); (1==denominator(p) && isprime(p)); }; \\ Antti Karttunen, Feb 25 2022
CROSSREFS
KEYWORD
nonn,look
AUTHOR
Joseph L. Pe, Dec 10 2001
EXTENSIONS
Terms a(10) to a(14) from Jonathan Sondow, Nov 22 2012
Extended by T. D. Noe, Nov 26 2012
STATUS
approved