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

 

Logo

Invitation: celebrating 50 years of OEIS, 250000 sequences, and Sloane's 75th, there will be a conference at DIMACS, Rutgers, Oct 9-10 2014.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A056683 Numbers n such that 40*R_n + 9 is prime, where R_n = 11...1 is the repunit (A002275). 1
2, 4, 5, 47, 107, 244, 1043 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also numbers n such that (4*10^(n+1)+41)/9 is prime.

LINKS

Table of n, a(n) for n=1..7.

Index entries for primes involving repunits

MATHEMATICA

Do[ If[ PrimeQ[40*(10^n - 1)/9 + 9], Print[n]], {n, 5000}]

CROSSREFS

Sequence in context: A154775 A210418 A167454 * A105288 A242915 A066684

Adjacent sequences:  A056680 A056681 A056682 * A056684 A056685 A056686

KEYWORD

hard,nonn

AUTHOR

Robert G. Wilson v, Aug 10 2000

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 September 2 23:10 EDT 2014. Contains 246369 sequences.