login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A056726 Numbers n such that 9*10^n + R_n is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
2, 5, 20, 41, 47, 92, 161, 401, 455, 8570, 18592, 73714, 78635, 100780 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also numbers n such that (82*10^n-1)/9 is prime.

LINKS

Table of n, a(n) for n=1..14.

Makoto Kamada, Prime numbers of the form 911...11.

Index entries for primes involving repunits

MATHEMATICA

Do[ If[ PrimeQ[ 9*10^n + (10^n-1)/9], Print[n]], {n, 0, 5000}]

CROSSREFS

Cf. A002275, A093634.

Sequence in context: A247131 A192164 A244087 * A176042 A185593 A136899

Adjacent sequences:  A056723 A056724 A056725 * A056727 A056728 A056729

KEYWORD

hard,nonn

AUTHOR

Robert G. Wilson v, Aug 11 2000

EXTENSIONS

8570 from Hugo Pfoertner, Oct 22 2004

a(11)-a(14) from Robert Price, Dec 05 2014

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 May 14 06:35 EDT 2021. Contains 343879 sequences. (Running on oeis4.)