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!)
A099409 Numbers k such that 2*R_k + 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k. 3
0, 1, 3, 9, 15, 28, 64, 1168, 1695, 2362 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
Also numbers k such that (2*10^k + 43)/9 is prime.
a(11) > 50000. - Robert Price, Oct 27 2014
LINKS
FORMULA
a(n) = A056677(n-1) + 1.
MATHEMATICA
Do[ If[ PrimeQ[ 2(10^n - 1)/9 + 5], Print[n]], {n, 0, 5000}]
PROG
(Magma) [n: n in [0..1000] | IsPrime( 2*(10^n - 1) div 9 + 5)]; // Vincenzo Librandi, Oct 28 2014
CROSSREFS
Sequence in context: A280963 A122819 A056287 * A002127 A357764 A061810
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Oct 14 2004
EXTENSIONS
Added a(1)=0, adapted Mathematica program, Vincenzo Librandi, Oct 28 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 06:56 EDT 2024. Contains 370953 sequences. (Running on oeis4.)