login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A193072 Odd numbers N for which numerator(sigma(N^2)/N^2) is prime but sigma(N^2) is composite. 1
39, 507, 2379, 6591, 13167, 29511, 148955, 1672209, 8852259, 212370543, 1929229929 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(12) > 10^10. - Lucas A. Brown, Apr 12 2021

LINKS

Table of n, a(n) for n=1..11.

PROG

(PARI) forstep(N=1, 1e7, 2, isprime(numerator(sigma(N^2)/N^2)) && !isprime(sigma(N^2)) && print1(N", "))

CROSSREFS

Intersection of A193066 and A193071.

Sequence in context: A231993 A229517 A254871 * A077454 A142976 A200409

Adjacent sequences:  A193069 A193070 A193071 * A193073 A193074 A193075

KEYWORD

nonn,hard,more

AUTHOR

M. F. Hasler, Jul 15 2011

EXTENSIONS

a(8)-a(10) from Donovan Johnson, Sep 19 2011

a(11) from Lucas A. Brown, Apr 12 2021

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 29 12:57 EDT 2022. Contains 357090 sequences. (Running on oeis4.)