The OEIS mourns the passing of Jim Simons and is grateful to the Simons Foundation for its support of research in many branches of science, including the OEIS.
The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A256711 Numbers k such that R_k - 10 is prime, where R_k = 11...1 is the repunit (A002275) of length k. 0
 3, 8, 12, 17, 86, 146, 1428, 1949, 4809, 16922, 33102, 125792, 211610 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also, numbers k such that (10^k - 91)/9 is prime. Terms from Kamada data. a(14) > 2.5*10^5. LINKS Table of n, a(n) for n=1..13. Makoto Kamada, Near-repdigit numbers of the form AA...AABA. Makoto Kamada, Prime numbers of the form 11...1101. Index entries for primes involving repunits. EXAMPLE For k=3, R_3 - 10 = 111 - 10 = 101 which is prime. MATHEMATICA Select[Range[0, 250000], PrimeQ[(10^# - 91)/9] &] PROG (Magma) [n: n in [0..1400] | IsPrime((10^n-91) div 9)]; // Vincenzo Librandi, Apr 09 2015 CROSSREFS Cf. A002275. Sequence in context: A190374 A189758 A190368 * A219635 A063225 A213238 Adjacent sequences: A256708 A256709 A256710 * A256712 A256713 A256714 KEYWORD more,hard,nonn AUTHOR Robert Price, Apr 08 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.

Last modified May 18 03:36 EDT 2024. Contains 372618 sequences. (Running on oeis4.)