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 A102997 Numbers n such that 4*10^n + 8*R_n - 7 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
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 OFFSET 1,2 COMMENTS Also numbers n such that (44*10^n-71)/9 is prime. No other terms below 10^5. a(3) > 2*10^5. - Robert Price, Oct 15 2015 a(3) > 8*10^5, if it exists! - Robert Price, Dec 31 2016 LINKS Makoto Kamada, Prime numbers of the form 488...881. FORMULA a(n) = A101734(n) + 1. MATHEMATICA Do[ If[ PrimeQ[(44*10^n - 71)/9], Print[n]], {n, 10000}] PROG (PARI) for(n=0, 1000, if(isprime((44*10^n-71)/9), print1(n", "))) \\ Altug Alkan, Oct 15 2015 CROSSREFS Cf. A002275, A101734. Sequence in context: A025038 A028684 A212928 * A252251 A139662 A140030 Adjacent sequences:  A102994 A102995 A102996 * A102998 A102999 A103000 KEYWORD bref,more,nonn AUTHOR Robert G. Wilson v, Jan 17 2005 STATUS approved

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Last modified August 23 11:47 EDT 2019. Contains 326222 sequences. (Running on oeis4.)