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

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A259138 Numbers k such that R_k + 7*10^k + 6 is prime, where R_k = 11...11 is the repunit (A002275) of length k. 0
 0, 10906, 499210 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also, numbers k such that (64*10^k + 53)/9 is prime. Terms from Kamada data. Note that Kamada does not recognize k=0 as 13 is a degenerate case of form ABB..BBA. a(4) > 1.2*10^6. LINKS Makoto Kamada, Near-repdigit numbers of the form ABB...BBA. Makoto Kamada, Prime numbers of the form 711...117. EXAMPLE For k=10906, R_k + 7*10^k + 6 = R_10906 + 7*10^10906 + 6 = 711...117 which is prime. MATHEMATICA Select[Range[0, 1200000], PrimeQ[(64*10^#+53)/9] &] CROSSREFS Cf. A002275. Sequence in context: A083513 A084277 A307873 * A082710 A240604 A065322 Adjacent sequences: A259135 A259136 A259137 * A259139 A259140 A259141 KEYWORD nonn,bref,more,hard AUTHOR Robert Price, Jun 18 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 November 29 15:30 EST 2022. Contains 358431 sequences. (Running on oeis4.)