login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A066111 Prime powers m such that sigma_4(m^2)/sigma_2(m^2) is prime. 2
2, 3, 5, 13, 17, 31, 43, 61, 83, 109, 121, 125, 131, 229, 239, 257, 263, 269, 311, 313, 343, 361, 443, 463, 503, 571, 593, 599, 619, 641, 647, 653, 659, 701, 797, 811, 853, 953, 967, 1009, 1031, 1039, 1063, 1123, 1373, 1459, 1483, 1499, 1663, 1669, 1693 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers m = p^w such that A001159(m^2)/A001157(m^2) is prime, i.e., m^2 is in A066109.

Also m is the square root of a term from A066109 (omitting the term 20). Apart from 20, up to 10000000 A066109 consists of squares of prime powers.

LINKS

Table of n, a(n) for n=1..51.

EXAMPLE

m=125: m^2 = 15625 = A066109(13), sigma_4(15625) = 59700165039453751, sigma_2(15625) = 254313151, sigma_4/sigma_2 = 234750601 = A066110(13) is prime. Observe also that sigma_2 is close to sigma_4/sigma_2.

CROSSREFS

Cf. A001157, A001159, A066109, A066110.

Sequence in context: A284669 A154554 A105879 * A065820 A163268 A235624

Adjacent sequences:  A066108 A066109 A066110 * A066112 A066113 A066114

KEYWORD

nonn

AUTHOR

Labos Elemer, Dec 06 2001

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 18 16:32 EDT 2019. Contains 322209 sequences. (Running on oeis4.)