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

 

Logo

Annual Appeal: Today, Nov 11 2014, is the 4th anniversary of the launch of the new OEIS web site. 70,000 sequences have been added in these four years, all edited by volunteers. Please make a donation (tax deductible in the US) to help keep the OEIS running.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A171130 Primes p such that sum of divisors of p+2 is prime. 3
2, 7, 23, 727, 2399, 5039, 7919, 17159, 28559, 29927, 85847, 458327, 552047, 579119, 707279, 1190279, 3418799, 3728759, 4532639, 5166527, 5331479, 7447439, 10374839, 24137567, 25877567, 28398239, 30260999, 43546799, 47458319, 52258439, 56957207, 62425799 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..32.

EXAMPLE

Divisors[2+2]={1,2,4}->7, Divisors[7+2]={1,3,9}->13, Divisors[23+2]={1,5,25}->31, Divisors[727+2]={1,3,9,27,81,243,729}->1093,..

MAPLE

with(numtheory): A171130:=n->`if`(isprime(n) and isprime(sigma(n+2)), n, NULL): seq(A171130(n), n=1..10^5); # Wesley Ivan Hurt, Sep 30 2014

MATHEMATICA

f[n_]:=Plus@@Divisors[n]; lst={}; Do[p=Prime[n]; If[PrimeQ[f[p+2]], AppendTo[lst, p]], {n, 10!}]; lst

Select[Prime[Range[700000]], PrimeQ[DivisorSigma[1, #+2]]&] (* Harvey P. Dale, Jun 23 2011 *)

PROG

(PARI) lista(nn) = forprime(p=2, nn, if (isprime(sigma(p+2)), print1(p, ", "))); \\ Michel Marcus, Sep 30 2014

CROSSREFS

Sequence in context: A032264 A139522 A163158 * A112089 A075062 A022497

Adjacent sequences:  A171127 A171128 A171129 * A171131 A171132 A171133

KEYWORD

nonn

AUTHOR

Vladimir Joseph Stephan Orlovsky, Dec 04 2009

EXTENSIONS

More terms from Michel Marcus, Sep 30 2014

STATUS

approved

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

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

Last modified December 21 01:10 EST 2014. Contains 252291 sequences.