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!)
 A056701 Numbers k such that 2*10^k + 3*R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k. 1
 0, 1, 2, 3, 4, 10, 16, 22, 53, 91, 94, 106, 138, 210, 282, 522, 597, 1049, 2227, 6459, 10582, 18895, 41269, 50702, 53185, 59796, 101395, 116514, 137551, 153116 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Also numbers k such that (7*10^k - 1)/3 is prime. a(31) > 3*10^5. - Robert Price, Oct 19 2014 LINKS Table of n, a(n) for n=1..30. Makoto Kamada, Prime numbers of the form 233...33. Index entries for primes involving repunits MATHEMATICA Do[ If[ PrimeQ[ 2*10^n + 3*(10^n-1)/9], Print[n]], {n, 0, 15001}] CROSSREFS Cf. A002275, A093672. Sequence in context: A183527 A085934 A220402 * A365352 A285190 A055506 Adjacent sequences: A056698 A056699 A056700 * A056702 A056703 A056704 KEYWORD hard,nonn,more AUTHOR Robert G. Wilson v, Aug 10 2000 EXTENSIONS a(22)-a(26) from Kamada data by Robert Price, Oct 19 2014 a(27)-a(30) from Robert Price, May 31 2023 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 09:54 EDT 2024. Contains 372620 sequences. (Running on oeis4.)