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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A002270 Composite n such that n*sigma(n) == 2 (mod phi(n)). 1
4, 6, 22 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Composite terms of A051948.

REFERENCES

J. Roberts, Lure of the Integers, Math. Assoc. America, 1992, p. 147.

M. V. Subbarao, On two congruences for primality. Pacific J. Math. 52 (1974), 261-268.

LINKS

Table of n, a(n) for n=1..3.

MATHEMATICA

Select[Range[4, 100], ! PrimeQ[#] && Mod[#*DivisorSigma[1, # ] - 2 , EulerPhi[#]] == 0 &] (* Jean-Fran├žois Alcover, Sep 16 2013 *)

CROSSREFS

Cf. A051948.

Sequence in context: A151520 A282517 A227249 * A286358 A088228 A272309

Adjacent sequences:  A002267 A002268 A002269 * A002271 A002272 A002273

KEYWORD

nonn,fini,full,bref

AUTHOR

N. J. A. Sloane.

EXTENSIONS

Definition corrected by Tanya Khovanova, Nov 05 2007

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified August 22 03:23 EDT 2017. Contains 290942 sequences.