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

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A074386 Numbers n such that sigma(n) is the square of a prime. 2
3, 81, 400 (list; graph; refs; listen; history; internal format)
OFFSET

1,1

COMMENTS

The next term, if it exists, is > 10^6.

The next term, if it exists, is > 10^7. - N. J. A. Sloane (njas(AT)research.att.com), May 26 2008

The next term, if it exists, is > 4*10^9. [From Sean A. Irvine (sairvin(AT)xtra.co.nz), Mar 25 2010]

EXAMPLE

sigma[{3,81,400}]={4,121,961}.

MATHEMATICA

Do[s=DivisorSigma[1, n]; If[PrimeQ[Sqrt[s]], Print[n]], {n, 1, 1000000}] (Corrected by N. J. A. Sloane (njas(AT)research.att.com), May 26 2008)

CROSSREFS

Cf. A000203, A001248, A023194, A028982.

Sequence in context: A197248 A183265 A137994 * A116009 A068562 A123656

Adjacent sequences:  A074383 A074384 A074385 * A074387 A074388 A074389

KEYWORD

nonn,bref,more

AUTHOR

Labos E. (labos(AT)ana.sote.hu), Aug 22 2002

EXTENSIONS

Definition corrected by Juan Lopez, May 26, 2008

Edited by N. J. A. Sloane (njas(AT)research.att.com), May 26 2008

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Puzzles | Hot | Classics
Recent Additions | More pages | Superseeker | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified February 15 03:11 EST 2012. Contains 205694 sequences.