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!)
A256762 Numbers k such that R_k + 80 is prime, where R_k = 11...1 is the repunit (A002275) of length k. 0
3, 6, 27, 30, 108, 119, 209, 444, 1050, 15189, 16401, 81363, 134385, 135011 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Also, numbers k such that (10^k + 719)/9 is prime.
Terms from Kamada data.
a(15) > 2.5*10^5.
LINKS
EXAMPLE
For k=3, R_3 + 80 = 111 + 80 = 191 which is prime.
MATHEMATICA
Select[Range[0, 250000], PrimeQ[(10^# + 719)/9] &]
PROG
(Magma) [n: n in [2..300] | IsPrime((10^n+719) div 9)]; // Vincenzo Librandi, Apr 10 2015
CROSSREFS
Cf. A002275.
Sequence in context: A128437 A200654 A208665 * A064283 A266857 A014561
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Apr 09 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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 25 12:58 EST 2024. Contains 370328 sequences. (Running on oeis4.)