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 A099421 0 together with numbers k such that 8*R_k - 7 is a prime, where R_k = 11...1 is the repunit (A002275) of length k. 2
 0, 3, 19, 79, 139, 223, 463, 544, 1096, 1419, 3247, 3877, 4417, 9507, 11091, 14602, 27811, 29188 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers k such that abs(8*10^k - 71)/9 is a prime. a(19) > 10^5. - Robert Price, Sep 06 2014 LINKS Makoto Kamada, Prime numbers of the form 88...881. FORMULA a(n) = A056664(n-1) + 1. MATHEMATICA Do[ If[ PrimeQ[ 8(10^n - 1)/9 - 7], Print[n]], {n, 0, 15000}] PROG (PARI) for(n=0, 10^4, if(ispseudoprime(abs(8*(10^n-1)/9-7)), print1(n, ", "))) \\ Derek Orr, Sep 06 2014 CROSSREFS Cf. A002275, A056664. Sequence in context: A240746 A027175 A093734 * A241885 A061171 A293561 Adjacent sequences:  A099418 A099419 A099420 * A099422 A099423 A099424 KEYWORD nonn AUTHOR Robert G. Wilson v, Oct 14 2004 EXTENSIONS a(17)-a(18) from Kamada data by Robert Price, Sep 06 2014 STATUS approved

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Last modified September 27 10:28 EDT 2021. Contains 347689 sequences. (Running on oeis4.)