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

 

Logo

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A098930 Numbers k such that 2*10^k + 5*R_k - 4 is prime, where R_k = 11...1 is the repunit (A002275) of length k. 1
2, 3, 5, 6, 12, 186, 435, 1746, 3447, 18798, 70209 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also numbers k such that (23*10^k - 41)/9 is prime.

a(12) > 10^5. - Robert Price, Mar 04 2015

LINKS

Table of n, a(n) for n=1..11.

Makoto Kamada, Prime numbers of the form 255...551.

Index entries for primes involving repunits.

FORMULA

a(n) = A101961(n) + 1.

EXAMPLE

If n = 3 we get 2551, which is prime.

MATHEMATICA

Do[ If[ PrimeQ[(23*10^n - 41)/9], Print[n]], {n, 0, 10000}]

CROSSREFS

Cf. A002275, A101961.

Sequence in context: A125877 A118787 A191783 * A075372 A064725 A301761

Adjacent sequences:  A098927 A098928 A098929 * A098931 A098932 A098933

KEYWORD

more,nonn

AUTHOR

Julien Peter Benney (jpbenney(AT)ftml.net), Oct 20 2004

EXTENSIONS

a(7) from Ray Chandler, Nov 04 2004

a(8) & a(9) from Robert G. Wilson v, Dec 17 2004

Addition of a(10) from Kamada data by Robert Price, Dec 13 2010

a(11) from Robert Price, Mar 04 2015

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 November 30 17:12 EST 2021. Contains 349424 sequences. (Running on oeis4.)