login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A056685 Numbers k such that 50*R_k + 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k. 2
0, 1, 7, 25, 65, 73, 232, 472, 539, 2773, 64714 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
Also numbers k such that (5*10^(k+1)-23)/9 is prime.
a(12) > 10^5. - Robert Price, Nov 13 2014
LINKS
FORMULA
a(n) = A099416(n) - 1. - Robert Price, Nov 13 2014 [adapted by Georg Fischer, Jan 04 2021]
MATHEMATICA
Do[ If[ PrimeQ[50*(10^n - 1)/9 + 3], Print[n]], {n, 0, 5000}]
Select[Range[0, 3000], PrimeQ[(5 10^(# + 1) - 23) / 9] &] (* Vincenzo Librandi, Nov 14 2014 *)
PROG
(Magma) [n: n in [0..400]| IsPrime((5*10^(n+1)-23)div 9)]; // Vincenzo Librandi, Nov 14 2014
CROSSREFS
Sequence in context: A127765 A155305 A155290 * A299262 A001296 A000970
KEYWORD
hard,nonn
AUTHOR
Robert G. Wilson v, Aug 10 2000
EXTENSIONS
a(11) derived from A099416 by Robert Price, Nov 13 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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 19 01:57 EDT 2024. Contains 370952 sequences. (Running on oeis4.)