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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A102972 Numbers n such that 3*10^n + 5*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 0, 1, 3, 6, 12, 33, 69, 111, 1965, 5646, 7404, 11103, 20790, 24840, 38199, 90669 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Also numbers n such that (32*10^n+13)/9 is prime. a(17) > 10^5. - Robert Price, Apr 07 2015 LINKS Table of n, a(n) for n=1..16. Makoto Kamada, Prime numbers of the form 355...557. Index entries for primes involving repunits. FORMULA a(n) = A101837(n-1) + 1. MATHEMATICA Do[ If[ PrimeQ[(32*10^n+13)/9], Print[n]], {n, 0, 10000}] Select[Range[0, 10000], PrimeQ[(32 10^# + 13) / 9 ] &] (* Vincenzo Librandi, Apr 08 2015 *) PROG (Magma) [n: n in [0..200] | IsPrime((32*10^n+13) div 9)]; // Vincenzo Librandi, Apr 08 2015 CROSSREFS Cf. A002275, A101837. Sequence in context: A026079 A066710 A033648 * A075209 A075207 A208131 Adjacent sequences: A102969 A102970 A102971 * A102973 A102974 A102975 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Dec 17 2004 EXTENSIONS Addition of a(12)-a(14) from Kamada data by Robert Price, Dec 13 2010 a(15) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013 a(16) from Robert Price, Apr 07 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 August 12 12:08 EDT 2024. Contains 375092 sequences. (Running on oeis4.)